I have an argument to make in favor of allowing legacy status for admissions. I am basing this on personal experience and some analysis of data done at similar schools when they were forced to release it due to lawsuits.
The way admissions works in the US now it has basically become a lottery for qualified students. We have more qualified students than we have seats at the top schools. The idea that there are some unqualified students who make it in only because their parents are alumni, at least at Stanford I have never seen. The top schools are all so competitive that they are all pretty similar and they would not do things to jeopardize their reputation or standing. So I think it's just not the case that there are unqualified legacy admits. At Harvard for example the legacy admits had higher SAT scores than the average admitted student which makes sense when you think about it. Children of alumni are probably better prepared for admissions.
So when choosing, Stanford might have to make a choice between two students with the same GPA, the same SAT score, the same interests, etc. and legacy status could decide it and I am ok with that. Building a campus network of people is a huge competitive advantage a school can have. You would be surprised how many people who are non legacy admits have pretty well known parents anyway or have parents who went to an extremely similar school. Singling out legacy admissions is not extremely meaningful and I don't think it's used to let in unqualified students at all.