I don't think that's the reason. That's one of the reasons. Sorta like how almost every serial killer had a brutal/weird childhood but not anyone with a weird childhood goes on to kill. I think you have to have some level of insanity in you and then the rest is the perfect environment to wanna go and kill. Also never underestimate the appeal of fighting for a "cause" rather then living as a cog in the "boring system"
Yes but in this case, the 'cause' involved killing infidels in a country far away from your own. ISIS were not exactly shy about telegraphing what they were doing in Iraq and Syria and some pretty otherwise normal people still decided to go over from the West, many of whom when caught somehow all seemed to be just butchers or engineers or doctors. God knows who was doing any actual fighting there.
I'm not sure people not changing their entire culture to hang out with a Muslim doctor is really the same as having a brutal childhood tbh and I can't see how that can in any way be used as a justification at all.
Kid gets raped by step dad when young, grows up to be a serial killer. I'm not justifying it but yes I can understand why he may have grown up with such a warped view of the world.
Muslim person grows up in the UK, grows up to become a doctor, doesn't get to go to the pub because they see it as against their religion, goes to join ISIS...nope, not the same for me. And I don't really know what people expect or want. Its engrained in British, American and European cultures, rightly or wrongly. A lot of hospital socials involve alcohol. Some non-drinkers still attend, some choose not to.
Either way, it should have about as much impact on their decision to join ISIS as their hair colour.