some ideas are dangerous to society, flat out. ie, "the institution of slavery was good because it's part of my cultural heritage".

University admissions are not just an issue of personal merit. It isn't something that you're owed because you did X, Y and Z. Colleges are trying to build a positive culture, just like startups, and that can involve rejecting skilled people with fringe beliefs.

Not to mention, who wants to pay $30,000/yr and have their kid be roommates with a holocaust denier?

People can believe whatever they want. They just can't work and go to school wherever they want