I suspect it might be an identity thing. He is a total loser and I suppose that belonging to a group that is seen as tough and dangerous gives him a sense of pride and a bit of self esteem he severely lacks.
Like I said he is British born and bizarrely considers himself to be "English"; he thinks that he is superior to fresh Pakistani/Afganistani/Somali etc. immigrants. Once he even told me to fuck off back to "my country".
Yeah it is an identity thing, but its more specific than that.
Do you remember doing chemistry at school and there was this thing you used to do about how when two elements are combined they create apeshit crazy results? Its like that. As children they are raised in a Muslim household where even at the most moderate they will be encouraged to view the world in very binary terms of Kuffar v Momin, the moral corruption of the non Islamic society. They'll have been raised with a basic moral framework that they will have just picked up tacitly, if nothing else, which places Muslim men as the highpoint of a hierarchical scale, underneath them are Muslim women, underneath them are non Muslim men, and beneath them, the lowest of the low, kuffar women.
Release that mindset into a liberal secular society that aspires to equality of men and women, and aspires to the (non political) benefits of cosmopolitanism and multi-culturalism (ie: all people no matter what their race or religion are equal - meaning Islam is no better than, say, Judaism or Hinduism or even Rastafarians), and you have the recipe for immense neurosis and anxiety and cognitive dissonance brewing between reality, and what they have been raised to believe, the atmospherics they have absorbed.
Add the hysterical victimhood culture of hardcore Islamist resentment and supremacist ideology, groups of others who have the same neurosis and notions as you to create a self-perpetuating echo chamber, and you have the chemical elements that spit, rage and explode in the heads of these pitiful men.