If you're looking for a diverse school, the University of Cincinnati is worth looking into. It's not the most ethnically diverse school out there, but the students, faculty, and staff come from a wide range of backgrounds, allowing students to not only learn in class but also learn about other cultures and lifestyles. A lot of UC students are from Cincinnati or within Ohio, but there are students who come from out of state and even from other countries. It's a great learning experience to meet international students because they learn from American students as much as we learn from them. Some colleges and programs tend to be more diverse than others, but with such a large campus, there are still opportunities for all students to interact.
The great thing about attending a large college is students aren't afraid to be themselves, and there are student groups on campus for almost every lifestyle. If there isn't, a new organization can be established. The University does a good job of allowing all ideas and groups to make their presence known, even if it is a very small minority of the campus population. Students are free to protest what they don't agree with. There are endless possibilities here to learn about other cultures, ideas, and lifestyles, which also help students determine who they are.