Yes. I think that's certainly a view that I'd endorse as well. If we are excluding people solely on the basis of a certain kind of disability, one has to ask the question why. It has to, in some way, be based on the suspicion that even if they're capable, they maybe have a diminished capacity. So there's a signalling that perhaps their ability to assess their own circumstances and options is suspect, whereas it wouldn't be for someone with a different kind of disability.
That does have the potential for fostering stigma about mental disorder, that their views are not to be taken as authentic and entitled to equal weight and credit as that of others.