It’s foolhardy to not give the children of your alumni who support your school and help the school’s rankings by doing so an advantage in admissions. It’s not like every kid wants to go to their parents’ alma mater, and there are no hard and fast rules saying someone else can’t go because a school accepted legacies. Maybe it’s different for public schools, but any private school that turns its back on a qualified legacy applicant deserves the hit in almuni donations they create.