I agree with you about the parents, and yes I've dealt with people on the spectrum. I used to date a girl who's little brother was severely autistic. Not functional, with the mind of a 5 year old. He was a sweet kid and I spent a lot of time with him.
Only from a cold logical standpoint can we say the parents are the cause of the attacks against Greta. That's just logical cause and effect.
But really the reason for the attack posts is because these people are absolutely bottom barrel garbage people. Unintelligent, unremorsful, discompassionate, apathetic pieces of shit. There is no other excuse for that kind of behavior.