Apologies if this question has been done or overdone before.
I have a couple of friends whose intense dislike of the X-Men seems to stem from one simple fact: they won't let non-mutants join the team. Using Spider-Man as an example, they say that they simply wouldn't let him join the team because he's not a mutant, and therefore, they're hypocrites/racists/whatever other harmful word you want to use there.
Now, I'm not aware of any specific instance when Spider-Man tried to join the X-Men, so if anyone knows about when he's tried, I'd be grateful to know. But I'm also curious if the larger question of if anyone has tried to join the team who was a non-mutant? I can't currently think of any stories where that's happened, either. What was the reaction, and the reason for it? Have the X-Men ever allowed someone one the team who wasn't a mutant (the combat teams--support personnel like Moira MacTaggart don't really count, imo).
Finally, I can't help thinking that, if it's true, there's plenty of justification for the X-Men wanting to keep their team mutants-only. But so far I'm only able to make an argument based on the fact that I feel this way. I'm having trouble stepping away from the racist/hypocrite label with any logical arguments. Anyone want to help me out here as well.