I think a lot of it is that the US doesn't take a paternalistic approach to mental healthcare or addiction treatment, so there are a lot of junkies and people with psychosis out on the streets in many cities. My understanding is that in Europe these people are more likely to be receiving some kind of treatment and be living in supported housing of some kind, whether mandatory or not, where in a lot of the US they are ranting and raving on the streets and on public transit. But, it's their freedom to refuse shelter and to refuse treatment (and our freedom to choose not to fund it).