The reason we should be paying for foster kids' college is because the state is their parent, so it's our responsibility. In a country that wasn't shit, regular people would be jealous of how kids who were wards of the state lived, and how well-raised they were. There's no clearer illustration of our values than the fact that children who, through no fault of their own, have become the responsibility of the state are treated like unwanted trash. The idea that a society like that could figure out how to ethically treat prisoners or immigrants is laughable.
Yet these are children, specifically, who deserve every opportunity we can afford them by default. Not “hopeless addicts” or some other group deemed not worth saving by so many of us, but people quite literally the epitome of worth saving. These people need every ounce of reassurance that we care and that they can integrate and function in society. That they deserve opportunity as anyone else does.
If we had to be self serving we could look at it like “each one of these people is statistically far more likely to be a burden on my own children in the future, so a small investment now could save a lot later”, but we seem to fail even in being selfish about it. I find this topic heart breaking.
Wards of the state: our responsibility, through no fault of their own.
Prisoners: our responsibility, their fault.
Immigrants: not our responsibility, but an indication of how well we can manage our economy. We should be able to put anybody who comes here to work.
Emigrants: we should let people leave who don't want to be here.
The first three are connected because there's no way to sustain providing anything for prisoners and immigrants that you don't provide for regular citizens. Wards of the state are the nation's children; there's nothing that normal citizens get that they shouldn't get. If they don't get anything, normal citizens are getting less than nothing.
People that really feel this responsibility become foster parents. But saying the state should deal with them isn't taking on that responsibility - at the end of the day actual people need to be their parents. I'm happy to support those people by having taxes directed their way, but the state doesn't get credit for their good deeds.