Short answer
Stay calm, stay kind, and do not let them push you away from Islam. The so-called haram police are Muslims who correct others harshly, often in public, and often over small things or things scholars disagree on. Many mean well, but their way is not the Prophet's (ﷺ) way. When a new Muslim spoke during the prayer, people glared at him and struck their thighs. The Prophet (ﷺ) did not scold him. He gently explained what the prayer is for (Sahih Muslim 537). He told Muslims to make things easy and not to drive people away (Sahih al-Bukhari 69). So if their advice is right, take it, even if it was said badly. If you are not sure, ask a scholar you trust. If they are harsh, answer with peace (25:63) and move on. Islam is learned step by step, and Allah (﷾) does not lay on anyone more than they can bear (2:286).
Full explanation
Who are the haram police?
Most new Muslims meet them sooner or later. Someone tells you off in front of others. Someone calls a thing haram that scholars actually disagree about. Someone judges you by your clothes or your accent. Many of them mean well and want to help. But the way they go about it is not the way of the Prophet (ﷺ). Allah (﷾) told him: "Wert thou severe or harsh-hearted, they would have broken away from about thee" (3:159). Harshness drives people away, and that is just what Allah (﷾) warned against.
“It is part of the Mercy of Allah that thou dost deal gently with them Wert thou severe or harsh-hearted, they would have broken away from about thee: so pass over (Their faults), and ask for (Allah's) forgiveness for them; and consult them in affairs (of moment). Then, when thou hast Taken a decision put thy trust in Allah. For Allah loves those who put their trust (in Him).”
How the Prophet (ﷺ) treated a new Muslim
Mu'awiya ibn al-Hakam had only just become Muslim. During the prayer a man sneezed, and Mu'awiya spoke out loud. The people stared at him and struck their thighs to make him stop. After the prayer, he says, the Prophet (ﷺ) did not scold him, hit him or insult him. He simply explained that talking does not belong in the prayer, which is for praising Allah (﷾) and reciting the Qur'an. Mu'awiya said he had never seen a better teacher (Sahih Muslim 537). Another time, a Bedouin, a man from the desert, began to urinate in the mosque, and the people grabbed him. The Prophet (ﷺ) told them to leave him and pour water over the place. Then he told them they were sent to make things easy, not difficult (Sahih al-Bukhari 220).
Mu'awiya ibn al-Hakam, newly Muslim, spoke aloud during the prayer when a man sneezed. The people stared at him and struck their thighs to silence him. After the prayer, he says, the Prophet (ﷺ) did not scold, beat or revile him, and he never saw a better teacher. The Prophet (ﷺ) told him that talking is not fitting in the prayer, which is for glorifying Allah, declaring His greatness and reciting the Qur'an.
Abu Hurayra reports that a Bedouin began to urinate in the mosque, and the people seized him. The Prophet (ﷺ) told them to leave him and to pour a bucket of water over the place, and said: you were sent to make things easy, not to make them difficult.
Islam is learned step by step
Nobody learns all of Islam in a day, and nobody is expected to. Aisha explained that the first parts of the Qur'an spoke about Paradise and the Fire. The rules on halal and haram came only after people had faith. If the first command had been to give up wine, she said, people would have refused (Sahih al-Bukhari 4993). When the Prophet (ﷺ) sent Mu'adh to Yemen, he told him to teach belief in one God (﷾) first, then the five daily prayers, then zakat, the yearly charity (Sahih al-Bukhari 1458). He also said the religion is easy, and anyone who makes it too hard for himself will be overcome by it (Sahih al-Bukhari 39). The duties still apply to you, but no one expects you to know everything at once. Start with the basics: your belief, your prayer, and keeping away from the big sins. "On no soul doth Allah Place a burden greater than it can bear" (2:286).
Aisha explains the order of revelation: the first passages spoke of Paradise and the Fire; only when people had come to Islam were the rulings on the lawful and the unlawful revealed. Had the first command been to stop drinking wine or committing adultery, she says, people would have refused to give them up.
Ibn Abbas reports that when the Prophet (ﷺ) sent Mu'adh to Yemen, he told him to call the people first to worship Allah alone. When they knew that, he was to tell them of the five daily prayers; and when they prayed, of the zakat, taken from the rich and given to the poor.
Abu Hurayra reports that the Prophet (ﷺ) said: the religion is easy, and no one makes it too hard for himself without being overcome by it. So do not go to extremes; come as close to the right way as you can, and take the good news of reward.
“On no soul doth Allah Place a burden greater than it can bear. It gets every good that it earns, and it suffers every ill that it earns. (Pray:) "Our Lord! Condemn us not if we forget or fall into error; our Lord! Lay not on us a burden Like that which Thou didst lay on those before us; Our Lord! Lay not on us a burden greater than we have strength to bear. Blot out our sins, and grant us forgiveness. Have mercy on us. Thou art our Protector; Help us against those who stand against faith."”
If they are right, take the advice
Sometimes the haram police are right, even if they said it badly. The Prophet (ﷺ) said the religion is sincere advice (Sahih Muslim 55). Good advice is a gift, whoever brings it and however it is wrapped. So ask yourself one question: is what they said true? If it is, thank them and change. You do not have to like the way they said it.
Tamim al-Dari reports that the Prophet (ﷺ) said: the religion is sincere advice (nasiha). He was asked: to whom? He said: to Allah, to His Book, to His Messenger, and to the leaders of the Muslims and all their people.
If you are not sure, check
Not everything people call haram is haram. On some questions, such as where to place your hands in the prayer, or whether a woman must cover her face, the schools of Islamic law differ. The Qur'an says: "ask of those who possess the Message" (16:43). And when news comes to you, "ascertain the truth" (49:6). So it is fine to ask, politely: where does that come from? Then check with a qualified scholar or an imam you trust. Do not give up something allowed because one person told you off. And do not argue about something you have not checked yet.
“And before thee also the messengers We sent were but men, to whom We granted inspiration: if ye realise this not, ask of those who possess the Message.”
“O ye who believe! If a wicked person comes to you with any news, ascertain the truth, lest ye harm people unwittingly, and afterwards become full of repentance for what ye have done.”
Answer with peace
You do not have to win the argument. The Qur'an says that when the ignorant speak to the servants of the Most Gracious, they answer "Peace!" (25:63). It also says: "Repel (Evil) with what is better: Then will he between whom and thee was hatred become as it were thy friend and intimate!" (41:34). A smile, a calm thank you, and a promise to look into it usually end the matter. Many harsh people soften when they are met with kindness.
“And the servants of (Allah) Most Gracious are those who walk on the earth in humility, and when the ignorant address them, they say, "Peace!";”
“Nor can goodness and Evil be equal. Repel (Evil) with what is better: Then will he between whom and thee was hatred become as it were thy friend and intimate!”
Do not let them push you away
The haram police are not Islam. They are people, and people make mistakes. The Prophet (ﷺ) said: make things easy and do not make them hard; give good news and do not drive people away (Sahih al-Bukhari 69). Even Mu'adh, a leading Companion, was told off for making the prayer too long for the people behind him. Are you putting people to trial? the Prophet (ﷺ) asked him, three times (Sahih al-Bukhari 705). Allah (﷾) does not look at your face or your wealth, but at your heart and your deeds (Sahih Muslim 2564). Find kind company: a mosque with a class for new Muslims, and friends who help you grow.
Anas ibn Malik reports that the Prophet (ﷺ) said: make things easy for people and do not make them hard; give them good news and do not drive them away.
Jabir ibn Abdullah reports that Mu'adh led a night prayer with a very long recitation, and a man who had joined it left. Mu'adh spoke against him, and the man complained to the Prophet (ﷺ). The Prophet (ﷺ) said to Mu'adh three times: are you putting people to trial? He told him to recite shorter chapters, because the old, the weak and the needy pray behind him.
Abu Huraira reports that the Prophet (ﷺ) said: Allah does not look at your faces or your wealth, but He looks at your hearts and your deeds.
And one day, do not become one
As you learn, you will see others make mistakes too. When you do, remember how it felt. Advise gently, in private, and only about what you are sure of. The Qur'an says: "spy not on each other behind their backs" (49:12), and "Let not some men among you laugh at others" (49:11). The Prophet (ﷺ) said: do not look for other people's faults (Sahih al-Bukhari 6064). And he said that Allah (﷾) is gentle and loves gentleness, and gives for gentleness what He does not give for harshness (Sahih Muslim 2593).
“O ye who believe! Avoid suspicion as much (as possible): for suspicion in some cases is a sin: And spy not on each other behind their backs. Would any of you like to eat the flesh of his dead brother? Nay, ye would abhor it”
“O ye who believe! Let not some men among you laugh at others: It may be that the (latter) are better than the (former): Nor let some women laugh at others: It may be that the (latter are better than the (former): Nor defame nor be sarcastic to each other, nor call each other by (offensive) nicknames: Ill-seeming is a name connoting wickedness, (to be used of one) after he has believed: And those who do not desist are (indeed) doing wrong.”
Abu Hurayra reports that the Prophet (ﷺ) said: beware of suspicion, for suspicion is the most false of talk. Do not look for others' faults, do not spy, do not envy, hate or cut off one another, and be brothers, servants of Allah.
Aisha reports that the Messenger of Allah (ﷺ) said: Aisha, Allah is gentle and loves gentleness, and He grants for gentleness what He does not grant for harshness, nor for anything else.
Perspectives
Some Muslims believe every wrong must be called out at once
Some Muslims say you must correct a wrong as soon as you see it. They say it does not matter where you are or how you do it, because staying silent is a sin.
The Prophet (ﷺ) told us to change a wrong with our hand or our tongue (Sahih Muslim 49).
Rebuttal
Yes, correcting a wrong is a duty. But the same Prophet (ﷺ) showed how to do it. He stopped the people who grabbed the Bedouin, and told them they were sent to make things easy (Sahih al-Bukhari 220). Allah (﷾) says to call people "with wisdom and beautiful preaching" (16:125). A correction that drives someone away from Islam has not removed a wrong. It has added a bigger one.
Being gentle means letting sin go.
Rebuttal
The Prophet (ﷺ) did correct people. He told Mu'awiya that talking does not belong in the prayer (Sahih Muslim 537). He corrected the act without crushing the person. And he said gentleness gains what harshness never does (Sahih Muslim 2593).
The Islamic perspective
Correcting a wrong is part of Islam. But it must be done the Prophet's (ﷺ) way: gently, wisely, and only about what is clear. A new Muslim should take good advice and check what they are unsure of. They should answer harshness with peace, and learn step by step.
The Prophet (ﷺ) corrected a new Muslim without a single harsh word.
Islam was taught step by step: belief first, then prayer, then the rest.
Good advice should be taken, however it is given.
Where scholars differ, follow a qualified scholar you trust, and do not condemn those who follow another.