Then the schooling will not be free, it will have a cost. Hiring a professional teacher or using for online courses is not free.You seem to be assuming the parents will be teaching. In fact a lot of parents form teaching collectives and hire professional teachers. Also there's a bunch of good online courses for kids of all ages that require minimal input from parents. Most homeschoolers are using these.
A benefit would be if parents pay attention, they can keep any crap indoctrination from happening.