> but we'll almost certainly see a drop in the number of young people attending college, since there's no "need".

More likely the opposite. Making $12K/year sucks. You can make $12K/year + 17K/year by flipping burgers, but that still sucks. Much better to go to college and then make $12K/year + 70K/year.

And a UBI allows more people to do that because it reduces the risk of quitting a bad job to go to school.