> most people don’t plan like this.

This is a pretty naive take. It is a $85k per year cost. If you can shift some money around and avoid $85k per year, you would absolutely do that.

> you could also emancipate your 17 year old.

This is complicated. Emancipation is not a “sign a form” kind of thing. The kid would have to be living completely independently (no support from the parents) and would have to convince a judge that they need to have rights and responsibilities otherwise given to adults. “Because the parents don’t want to pay for school” isn’t really a valid reason.