If you have not yet realized it, here is a black pill for you: most people are deeply manipulative and bullying basically all the time. For example nearly all social rules that are commonly accepted in society are basically about which kinds of manipulations and bullying of other people are accepted by most people vs not.
With this in mind, the answer to your question
> So why harass autistic people?
is trivial: because it is currently socially mostly accepted.