I think what Muni in SF has done with putting cameras and microphones everywhere has kept the thug problem under control. I used to ride Muni a lot before that and would regularly watch and overhear people graffiting, planning some sort of gang violence, screaming in ecstacy while obviously extremely high after refilling their opioid prescription at sf general, openly smoking their crack rocks across from me, etc. That's why people don't ride public transit.