Dysphoria is the correct term here. Whatever the cause, whether it's autism or something biological, Chris is viscerally bothered by having a penis. He wants to cut it off. That is not normal. He's severely fucked in the head.
Same way that people with BIID have dysphoria about having a normal count of limbs.
I think you're confusing Chris being weird and funny (which he is) for a lack of legitimacy. It's the same thing with Barb abusing him. Chris is a dipshit and a shitty person himself, but that doesn't mean there isn't a shittier person, an actual abuser, sitting behind him.
How much of an "excuse" circumstances and mental illnesses are isn't ever a straightforward question.
I think almost all of us would agree with the following statements:
1) Chris' life is pretty fucked up.
2) Chris' autism has hampered him his whole life, and contributed to 1).
3) His mother, and to a lesser extend his father, has hampered him his whole life, and contributed to 1).
4) He has some other issues, which may be in part a function of 2) and 3), which also contribute to 1)
5) He has made some poor choices, which he did not have to make, which contribute to 1).
2), 3), and 4) contribute to 5), but not entirely. Most of the poor decisions could have been avoided, despite his various issues, but his issues did make him more susceptible to them. So how much blame does he get? I don't think either extreme is right. It isn't right to say nothing is his fault. But it isn't right to judge him as harshly as someone who didn't have the issues Chris has, but still had as many fuck-ups.
Then again, it is fair to say that anyone with as many fuck-ups as Chris must have some serious issues. But if you follow that logic too far, you end up with the argument that anyone who fucks up does so because of issues they have, so by definition can't be blamed for it. For example, I agree with your premise that Barb is a really destructive force in Chris' life. But it is clear from her hoarding that she has some serious issues. Could her mistreatment of Chris stem from similar pathologies as the hoarding? Seems quite possible. But if that means she is off the hook entirely, noone is ever to blame for anything.
