1) For many people, "more affordable public school" is still out of reach.

2) The quality of education at public schools is very often lower than that at more expensive schools. I have at least two data points of my own experience to back that up, along with the public perceptions. Acting like getting a better education is a "bad choice" because privatized universities overcharge students is not only an oversimplification, but one that punishes people for trying to better themselves, and for trying to be better contributors to the society we all share.

3) From what I've read, it is legal, via the HEROES act of 2003.