Why does Islam forbid Muslims to imitate disbelievers?
Question

Why does Islam forbid Muslims to imitate others?
Praise be to Allah.Imitating others is something that happens to humans. It is indicative of great love of the one whom one imitates, but in many cases it is an unhealthy phenomenon. Islam pays a great deal of attention to this issue (Muslims imitating disbelievers), and the Messenger (blessings and peace of Allah be upon him) definitively prohibited it and said: “Whoever imitates a people is one of them.” Narrated by Abu Dawood (4031); classed as saheeh by al-Albani in Saheeh Abi Dawood.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
At the very least this hadith indicates that it is prohibited to imitate them, even though the apparent meaning indicates that the one who imitates them is himself a disbeliever, as in the verse in which Allah says (interpretation of the meaning):
“And if any amongst you takes them [Jews and Christians] as Auliya [friends, protectors, helpers, etc.], then surely he is one of them” [Al-Maa’idah 5:51].
This may be referring to imitating them in everything, in which case this constitutes disbelief, which dictates that it is haram to imitate them in some matters. Or it may be interpreted as meaning that he is one of them to the extent to which he is imitating them, so if it is disbelief or a sin or a symbol that is unique to them, then the ruling is like that. Whatever the case, it implies that imitating them is haram."(Iqtida’ as-Siraat al-Mustaqeem  1/270-271)
We can see the wisdom behind the prohibition on Muslims imitating disbelievers if we understand the harm to which this imitation may lead and the bad consequences thereof, which include the following
1. If a Muslim imitates the disbelievers, it indicates that he prefers the way the disbeliever looks to the way he himself looks, and this may be an implicit objection to the law and will of Allah, may He be exalted.
If a woman imitates a man, it is as if she is objecting to the appearance with which Allah has created her, and is not pleased with it. By the same token, when a Muslim imitates a disbeliever, it is as if he is saying that the appearance of the disbeliever is better for him than the appearance with which Allah has honoured him and has commanded him to keep.
2. Imitating someone else is indicative of a sense of inferiority and psychological defeatism, but Islam does not accept for the Muslims to declare such defeat, even if it is real.
Admitting and declaring defeat increases the weak person in weakness, and increases the strong person in strength. This may be one of the greatest obstacles to the weak person rising up and rectifying his situation.
Therefore people of mature thinking in any nation or community object to their people imitating their enemies; rather they are keen to make them distinct on the basis of their heritage, customs and dress, even if they think that the enemy has better heritage, customs and dress than what they have. That is only because they understand the psychological and social impact – and even the political impact – of outwardly imitating the enemy.
3. Imitating others in outward appearance implies love and loyalty towards them, because a person does not imitate anyone except those whom he loves. But the Muslims are commanded to disavow the disbelievers of all types. Allah, may He be exalted, says (interpretation of the meaning):
“Let not the believers take the disbelievers as Auliya (supporters, helpers, etc.) instead of the believers, and whoever does that will never be helped by Allah in any way, except if you indeed fear a danger from them. And Allah warns you against Himself (His Punishment), and to Allah is the final return” [Aal ‘Imraan 3:28]
“You (O Muhammad (blessings and peace of Allah be upon him)) will not find any people who believe in Allah and the Last Day, making friendship with those who oppose Allah and His Messenger (Muhammad (blessings and peace of Allah be upon him)), even though they were their fathers, or their sons, or their brothers, or their kindred (people).” [Al-Mujaadilah 58:22].
And the Prophet (blessings and peace of Allah be upon him) said: “The strongest bonds of faith are loyalty for the sake of Allah, enmity for the sake of Allah, love for the sake of Allah and hate for the sake of Allah.” Narrated by at-Tabaraani and classed as saheeh by al-Albani in as-Silsilah as-Saheehah (998).
Shaykh al-Islam Ibn Taymiyah said in Iqtida’ as-Siraat al-Mustaqeem (1/549):
Outward imitation leads to a type of love and feeling close in one’s heart, just as love in one’s heart leads to outward imitation. This is something that we see in real life. End quote.
Imitation of the disbelievers weakens this principle, which is one of the principles of Islam, namely disavowing and despising the disbelievers.
4. Outward imitation of the disbelievers leads to something that is more serious, which is imitation of them in one’s heart and adopting their beliefs, or regarding their views and ideology as sound. There is a clear connection between outward appearance and what is in the heart, and the one affects the other.
Shaykh al-Islam Ibn Taymiyah said in Iqtida’ as-Siraat al-Mustaqeem (1/548):
Imitating others and being like them in outward appearance and behaviour leads to imitating them and being like them in one’s heart and mind, by way of gradual, hidden influence. We have seen that the Jews and Christians who mix with the Muslims are milder in terms of disbelief than others, just as we have seen that Muslims who mix a great deal with the Jews and Christians are weaker in terms of faith than others. End quote.
Ibn al-Qayyim (may Allah have mercy on him) said:
Because imitation in outward appearance may lead to being influenced with regard to thought and beliefs, as is indicated by Islamic teachings, common sense and real life. Therefore Islamic teaching disallows imitating disbelievers, animals, devils, women and Bedouin."(Al-Faroosiyyah (p. 122).
These are some of the clear reasons for the Islamic prohibition on Muslims imitating the polytheists. The Muslim has to comply with the rulings of Allah, may He be exalted, and believe that Allah, may He be exalted, will never command him to do anything but that which is wise, in his best interests, and will lead to his happiness in this world and the hereafter.
And Allah knows best.