My sister is on the spectrum, and she agrees with the idea that autism is a mental disorder. What she disagrees with is calling anyone on the spectrum "disordered". So she'd agree with you that most autistic people shouldn't be labeled that way, but disagree that no autistic people should be.

Even at her low end of the spectrum, it can cause a lot of distress and pain. I guess it just depends on a person's particular case and the circumstances of their life.