I'm going to make an argument for linguistic descriptivism. I've never once thought, in the WSB subreddit, someone calling another an "autist" or a "retard" was ever intended to harm or disrespect people with those literal issues. It's a niche audience with very specific meaning. As a linguist, I find it fascinating and aptly descriptive frankly. As a person who knows people with actual mental problems, I understand why it may be distasteful. However I strongly feel that when you enter that subreddit, the jargon is both incredibly obvious and specific.