Permitted by the group home they live in, or, if they’re not their own guardian, by their guardian. Sorry I wasn’t more clear.
If “Mike” had been on a no-alcohol diet due to prescription meds or his guardian forbidding it or whatever, and I facilitated his buying a beer, I’d have been fired in a heartbeat. Fortunately Mike’s mom was a doughty Irishwoman who liked to imbibe, so all was well.
In Illinois at least (as of a decade ago), officially a DD person has the same rights as a non-DD person - assuming those rights aren’t abrogated by the person’s guardian. Unofficially, depending on the group home they live in, those rights exist more on paper than they do in real life. One particular example that comes to mind is that of a man in his sixties who loved him some boobies. He had nudey posters on the walls of his private bedroom in the group home where he lived, as was his right. His devoutly Catholic, 90-something mother saw that and, once she regained consciousness, gave all of the caregivers present an earful. Then she called their boss and ripped her a new one. Then the posters came down. Totally illegal, and I suppose if anyone wanted to they could have made a phone call to the state agency that handles these things. But the group home just made it a general point to try to redirect the guy away from nudey posters just to keep peace. I’m not saying it’s right, but it happened (and likely still happens).