Because every single Asperger trait in isolation, from poor eye contact to obsessive interests to social fatigue, can occur in the NT population, people often say things like 'oh, my friend finds social situations tiring after about half an hour',intending to be nice but actually conveying a lack of true understanding. It feels like they are invalidating my experience, which is profoundly more significant than mere social fatigue!. It is like they are trying to say 'just pull yourself together, try harder and things will be fine', or that 'you are making too much of a fuss, even NTs struggle sometimes with social situations'. Yes, this is true, but really beside the point. It is a bit like saying to someone with ME, 'even people without ME feel really tired and run down sometimes'.
Why is this acceptable when talking about Asperger's?