People who have not been mentally ill have no idea at all what it is like. Trust me on this. I had no idea myself until it hit me. There are, of course, degrees of mental illness. My wife has a cousin who is just totally incapacitated and every so often has about six coppers out to overpower him and drag him to the hospital. You see, when he feels better, he stops taking his pills and goes back to square fucking one.
This lad used to be hard-working. Very much so. He was not one for fancies either. But one day, as he tells it, as he was driving his firm's van, cars started talking to him. He went missing for about three days, during which time he drove the van to all manner of infeasible places. He will never, ever be fit for work, never. His pills keep him calm, but take them away and he becomes an incredibly strong, violent, aggressive danger to the public.
The idea that he 'chose' to be like that is laughable. I'm certain he'd be delighted to be what he used to be, buying and selling his portfolio of shares and riding his motorbike at weekends. But he won't be. Chances are he'll die alone in a secure hospital.
If society put more resources into NHS mental health (especially psychiatrists) and if the country was more civilised, with less obsessive pressure at work, maybe, just maybe, this issue would resolve itself. But as usual, people will the end but not the means.