Are disabled people subhuman, because they don't have free mobility? Never said anything like that - only that your illness affects the reasoning, i.e. the will as well. It doesn't have to be all the time as there are different mental conditions affecting people differently at different times.
Many things can affect your reasoning, that is true. But the issue is how do you prove it, and if so, does it even matter what you prove if the person isn't harming anyone?
Coercing someone into psychiatric treatment in some facility until the person "is better" is open ended in nature that it might effectively mean imprisonment for life.
That's why there is (or should be) such a high barrier for this.
Don't get me wrong, I'm really happy for the family in this article and if I knew 100% for sure that (reasonable) action X and Y would have this positive outcome - I would do it.
But the problem is that more often than not you cannot know because we all can't read the minds of others.
There are cases of people living in (for us) unimaginable conditions by their own choice. And some of them are even willing to fight for their right to live in such a way.
