My response to this has been something like, how many people's lives should be wasted?
If a person needs full time care, is someone else giving up their life ok?

I would probably leave people in "school" until they were proficient enough to live on their own.

Some people will learn arithmetic in school, other's will learn how to put their clothes on properly.

But, this is only a luxury that we can afford because we have so much excess.
The way things worked out in olden times was the village idiot did chores like delivering messages and sweeping. Slept in a spare room. The village collectively cared for them.

Or, the idiot did something stupid and ended their lives.
Since we have made life so very very safe, this happens much less today.