The student population is mostly white. This is not necessarily a bad thing, and it's not uncommon for a small liberal arts college. The admissions staff does, however, try to bring in people from different backgrounds. The problem is, according to some people, that the College claims students of color and international students as an achievement, and they lump everyone together. As a student of color, I felt that I would have a lot of resources and support, and I have not been proven wrong. The administration does really listen to concerns. There are cultural houses on campus and cultural events. Many faculty of color are often willing to take students under their wings (although there aren't that many of them). All in all, though Mount Holyoke is good at recruiting people from lots of different backgrounds, there should be more of an emphasis of inclusion within the student community. If there were, the admissions staff would not have to try as hard. I have not heard of any serious racial incidents on campus, mostly just little misunderstandings.
Most Mount Holyoke students are from the Northeast. A few, certainly not the majority, come from wealthy backgrounds. Some of them got here on merit, I'm sure, but others are not that bright and there is a consensus that they were accepted because their parents paid the entire cost of admission. Most people here get some sort of financial aid. Unfortunately, not many people here are from working-class backgrounds. That's probably partly because MHC is no longer a need-blind school. That being said, most people I know are happy with financial aid.
Students are generally very nice to each other. Unfortunately, there is a lot of self segregation, but this phenomenon does not always occur on racial lines. Some people just realize they have common interests and they bond. Groups don't tend to be super exclusive, though.
Students do generally care about a lot of different causes. Unfortunately, sometimes they don't make the effort to support those causes. Worse still, they join causes and don't make connections between similar groups. Not everyone is aware of every issue, and, honestly, you can't expect everyone to be.
As far as LGBT culture on campus goes, there is a consensus that sexuality is fluid. There are some people who don't even bother to define it. Not everyone on campus is queer, though. They're a minority on campus, but they're very visible.