The key word here is "bully". It's also a tricky word because the line where bullying starts is often blurry. There's a context-dependent spectrum of gray that makes up the difference between bullying and calling someone out on assholeish behaviour. I think you're right that absolutist poisons don't work here.

My reading of the initial post was somewhat different than yours. I imagined the person saying "I would never bully someone for being autistic" as someone who believes themselves to be a Good Person(TM), despite engaging in bullying behaviours. My brain went there because I've known people like that. Maybe they would refrain from bullying someone who they knew as being autistic, but if they take that approach, they're going to inadvertently bully a heckton of autistic people for their autistic traits, just because they don't know they're autistic. I don't think that's okay.

I interpreted the original post as advocating for being more tolerant regardless of labels or identities, because often, we don't know the full context behind a behaviour. A complement to this is that being autistic doesn't exempt you from being an asshole. I want to be called out for shitty behaviour, but I don't want to be bullied.

I feel like I'm articulating my point badly, but something that's underlying this entire comment is a book I read a while back named "Racism without racists". It looks at racism as a product of the system, and how neutral or even good people can be a part of perpetuating it. Acknowledging this is a necessary and often uncomfortable step towards dismantling unjust systems and it doesn't mean that people are Bad People(TM). When people feel attacked and perceive "the system that we are a part of and that some of us benefit from is structurally racist" as being an accusation of "you are racist", it leads to them becoming defensive and refusing to acknowledge the address of the broken system.

I think ableism functions in a similar way. Society is ableist on so many levels, but I've found discussing this to be difficult when I have to walk on eggshells to avoid people becoming offended as if I have accused them of being ableist (even if I haven't used that word at all and am focussing on constructive discussions about way forwards). It feels hypocritical when people consider themselves an ally, but then have the audacity to take a basic access request like "please don't label the event as wheelchair accessible if it isn't" and make it about them, becoming outraged. My take on the original post is that it's directed at this kind of hypocrisy.