And disability is so stigmatized that when someone who is disabled also encounters racism/sexism/homophobia, observers dismiss the part disability plays.

re Homophobia: Lesbians are so rare they don't even show up on the lists :,)

Re: your last point, it's worth mentioning somewhere but maybe not here, the ableism that permeates "impairment cultures." That is, blind/deaf people who dismiss those who patronize by saying, "I'm strong as a bull!" Or wheelchair users who complain that people talk to them "as if they were stupid."