What's your alternative to "warehousing?" Send children to jobs?
As to the reasons for "shipping" people to college: a) they like it; b) it mostly works, even in our screwy society; c) brain science is finding that the frontal lobes don't finish maturing until the early 20s.
This is a topic where the left should simply advocate an education society, and save its kooky reforms for debates after the victory. We should be pushing to double the amount of GDP spent on schools and attacking the right's "reform" shit, which is a ruse to distract people from the only real issue: ACCESS to world-class teaching. That could be provided to everybody in a heartbeat, if we could put it on the agenda. Getting all wavy-gravy about the "oppression" of schools is an excellent way to torpedo ourselves. Let your great-grandchildren deal with that one. We have more basic troubles.