It is not permissible to kill resident or immigrant disbelievers
Question: Some young people think that it is lawful to alienate the Kafirs (disbelievers) residing in or immigrating to Muslim countries. Accordingly, some of them deem it lawful to kill and steal from them if they see them committing Munkar.
Answer:
It is not permissible to kill resident or immigrant Kafirs who are Musta’man (non-Muslim with a peace agreement permitting them to enter and stay temporarily in a Muslim country), who have entered into a country peacefully. It is also not permissible to kill or attack those who commit sins; the Munkar that they have committed should be referred to the Islamic Law Courts and the decision they see will be sufficient.
Question: What if there are no Islamic Law Courts?
Answer:
If there are no Islamic Law Courts, just give advice. Those in authority should be advised and guided to do good and they should be cooperated with to rule by the Shar‘ (Law) of Allah. It is not permissible for those giving advice and admonition to kill or punish; they should instead cooperate with those in authority in a way that is best so they can rule the Servants of Allah by the Shar‘ of Allah. Otherwise, the obligation is confined to giving advice, guiding to the good, and resisting Munkar in a way that is best. Allah (Exalted be He) says: “So keep your duty to Allâh and fear Him as much as you can” [Al-Taghabun: 16]
Those who are experienced and knowledgeable in such matters undoubtedly know that resisting evil by killing or beating results in worse corruption and evil.