Being fat is generally in one's control and being autistic is not.

Being on the autism spectrum could mean quite a few different things because the spectrum has become so broad. Many times the signs that a child is on that spectrum are difficult for parents to see within their own children. However, the earlier the identification and intervention the more you can help your child to be successful. If someone noticed something about your child that you hadn't noticed and it would both help your child and help you to be a better parent, wouldn't you want to know that?