[dragonwriter]

> We tend to focus on the lighter end of the spectrum, where people can lead functional and fulfilling lives.

There's a form of survivorship bias here: the greater the degree of impairment, the less broad social contacts the person is likely to have, so on average most people's experience is going to have people who have less severe impairments overrepresented compared to their relative frequency among those with the diagnosis.

And I'm sure most people that think about the issue recognize that on an intellectual level, but it's still difficult to tune out the effect that has on one’s “gut feeling” about the subject.