No, to assume that forgiveness or empathy to one autistic individual denigrates an entire spectrum of autistic individuals is the same as assuming that from the actions of one we can confer some sort of collective responsibility. This assumption is the root of all prejudice.
If you believe that some autistic people can be decent, though, it's no longer an excuse for Stallman that he's autistic. I'm on the spectrum myself, it's not a free pass for being offensive.
This is not clear to me. Many people are assholes but that’s by choice, not because they’re incapable of not being assholes.