Sure, I can see that, chances are you aren't actually saying someone has a mental condition. It all comes down to how you're using it I guess. I'm probably guilty of using "retarded" to describe...say...manga endings I disliked, but if I used that word to describe someone then I'd expect to be moderated. No one has the right to be a jerk, even if your intention isn't literal, there's no mystery what the implication is.
As far as the example you cited...honestly it seems classless to me and I don't find it very funny, and not sure why describing it as 'autistic' drives the joke home better. Maybe I'm just crazy. I think empathizing with people who might actually have that condition is never a bad thing though.
I'd agree, but not everyone is an empathetic person. It doesn't mean they hate autistic people or that they like to demean them, but some people just don't care enough to change the way they live.
If you want people to be understanding of you, then you have to try and understand them.