I meant to say BUY it. Either way, the argument is about people getting into universities on pure merit then legacies like every other 'edge' goes against that argument and isn't legitimate. A private institution can do whatever it wants.
I agree that at a state university unless the applicant is admitted purely on merit then the university isn't serving the state purpose it was established for. I also think that as long as affirmative action is there, legacy admissions should be, and that legacy admissions are far more legitimate than affirmative action.
That said, I expect you will be against athletic scholarships as well. And set-aside scholarships for specific major areas. And special loan and grant programs for specific major areas.
All of these work against the state purpose of generally increasing the populace's education, and instead, specifically for a state purpose of increasing graduates in some major areas, which works against the market, to my way of thinking.