Earlier quoted context omitted.
While there's truth to that, it's worth noting that most of those homeless people are suffering from ill mental health and/or substance dependence. You make it sound like they just shrugged and decided that that's the life they want, but I don't think that's how people end up homeless. There are decisions involved, but they're probably not quite as voluntary as that.
Those people are given help, but if they refuse that, there's nothing you can really do. People are only forced if they start being dangerous to other people.
I assume this isn't really true, and that the standard in Finland is that they're institutionalized if they're a danger to other people or themselves. The latter part is tricky, though. A person who is clearly in danger of killing themselves with a razor blade can be committed. A person who is in danger of drinking themselves to death on the sidewalk, perhaps not.