From what I've seen in average results in online tests, people with ASD, on average, do very slightly worse than NTs in recognising facial expressions.
There are two kinds of empathy: Cognitive empathy and Affective empathy.
Affective empathy is what's involved in recognising other people's emotions, and sometimes even "catching" them. It's my understanding that most people with ASD are have just about as good of Affective empathy as NTs. We can recognise that someone is sad and feel sorry for them. Being in the presence of such a person might even make us feel sad ourselves.
Cognitive empathy is the ability to see things from someone else's perspective. People with ASD are generally much worse at cognitive empathy than NTs.
I think, for me, one way that a lack of cognitive empathy manifests is that, although I might recognise that someone is sad and feel sorry for them, I won't have a clue what to do to comfort them; I'll tend to just stand around feeling awkward and being useless.
I also hate arguing, but I sure seem to do it a lot, presumably again because I have trouble seeing the other person's point of view.
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Level 1 Autism Spectrum Disorder / Asperger's Syndrome.