I think the best argument to be made is that if these drugs were used in safe settings under supervision of close friends/family the likelihood of anyone exacerbating their 'underlying mental illness' would be little to none.
IMO under these conditions almost anyone could have a profound psychedelic experience even if they are one of those people who 'doesn't like hallucinating.'
You could start with extremely small doses and titrate your way up so that the person can get used to the headspace before it became visual or simply use those small doses in the midst of other types of calming and soothing therapies.
The conditions you describe were met in this case (not quite a clinical or therepeuticalcsetting, but come on heh), and the the individual we're talking about isn't a hardcore psychonaut but certainly not drug naive and has tolerated high doses of in part far more powerful compounds remarkably well. Set and setting were as good as can be expected, or so I thought. I wouldn't have embarked on the venture if I had had any doubts about that, no way In view of my history.
For now I refrain from introducing people to psychs, though that is a bit of a non sequitur, but I'm shellshocked tbh. I'm far from fearmongering I hope, but one should be aware of the toll this kind of experiments can exact from healthy adults trying to be responsible going about it.
Edit: IamMe, I think you're taking unnecessarily offense with my choice of words, we're not that far apart actually. Allow me the idiosyncratic use of some words and keep in mind english isn'nt my native language. And well massive....browsing erowid and reading some threads here, I couldn't help using the word, haha. Anyway:
I think the whole statics based argument is a little bit beside the point. A bit like arguing that communism is worse than fascism by comparing the number of Hitlers and Stalins victims.
Skiing for example is a risky part time (I'm sticking to my flawed definition of the word, please excuse), people are getting injured, some of them killed, and many of those accidents could have been prevented by following simple safety-guidelines. Am I arguing the sport should be prohibited, or people generally discouraged to take it up? No, certainly not. Would I ever denie that it can be dangerous to exercise it? No, that would be completely foolish.
Of course the hospitals in my neck of the woods are full with patients dying from the longterm consequences of their alcohol abuse, thousands of them actually. Does that make the perils connected with the use of psychedelics look any more attractive? No, don't think so. I take them because they are infinitely more fascinating and rewarding than booze ever will be, and for me personally the risk is not neglieable but acceptable.