Ican, I'm sure that if someone made an offensive comment regarding your age, sex or race that you would be upset and wouldn't see it as a 'fad', it's no different if someone makes a comment like that about someone with a disability.
If someone told a black person they shouldn't use their skin colour as an 'excuse' about something, that would be horrible and offensive - it is the same saying that about someone using ASD as an 'excuse'.
I postulate that you don't see disabilism as a 'thing' because it doesn't affect you, and if course if something doesn't affect you then no one else should moan about it, right? I'm sure you are intelligent to know that other people outside your own bubble have different issue and needs, so how about trying to have a little bit more sympathy for your fellow human?
Oh, and by the way, just because you don't believe that disabilism is a word doesn't mean it isn't, you could say that you don't believe the name Brian isn't a real name, or that the word 'truculent' isn't a real word but you would be a twat wrong. Happily your opinion on what are real words and what aren't is irrelevant.
Fwiw my phone doesn't autocorrect diasabilist or disabilism so Apple at least believe it's real :D