Even those who are not, will probably develop some sort of schizophrenia due to their marginal lifestyle, but I wonder if it's really a "disease", I feel like it's an adaptation to their environment for people who are more sensitive than others. I feel like the pain is more due to the lack of solutions, especially in a city centre, where it's a constant hell for these guys (and for most any other animal actually, except a few who adapted to that: pigeons, rats, some insects but not the most beautiful ones), just my thought