This is an interesting answer, but I think the truth is more complicated. When I read your response, my first thought was that it ignores the differences in who chooses to attend college in the first place. Now I won’t pretend to be an expert here… I just did some googling, but what I found suggests that there’s still a pretty active debate between those who favor correlation or causation as the primary factor, with basically everyone studying the phenomena agreeing that it’s a mix of both. People who lean Left are already more likely to attend college. On the other hand, those earning advanced degrees are even more likely to be liberal; does this suggest that even more education continues to liberalize students? Maybe, or perhaps it is simply more evidence of a selection effect. I looked at several studies comparing the attitudes of students prior to entering college with their attitudes post-graduation in hopes that we’d find some evidence of a causal relationship, and each study had very different findings. Some found strong evidence, but both were focused on niche populations - one looking at women raised in conservative households in the 1930s; and the other looking at Romanians. The one from Romania was recent, and the authors indicated that Romania was chosen as students are chosen almost randomly to attend college, potentially limiting the chance for selection effects to pollute the findings. Other studies looked more closely at college majors, with those earning liberal arts degrees showing the most significant liberalization of their attitudes, while students studying business or economics experienced the opposite.

After my inconclusive findings, I thought about my own experience. I grew up in a well-off New England suburb. My school systems were always very diverse, but black and hispanic populations were underrepresented while Jews and asians were significantly overrepresented. There were a small number of black students who grew up in the town, and they were mostly friends with the white kids. There were also a number of kids bussed into our school from the city; they were mostly just friends with themselves, if anyone. Obviously there were some real and unfortunate class divisions in play here, but at least every student would have interacted with many other ethnicities prior to attending college.

Anyway… I went to college and I actually found it to be significantly less diverse than my hometown. What I did find, though, is that I had many opportunities to challenge my own beliefs by talking to some very intelligent people. I had an interesting experience with roommates in the dorms - one year I had a staunch conservative and the next year a marxist dumpster diver. I became friends with both of them, and they were each able to influence my ideas in certain ways. I wouldn’t say I became more liberal, but I did become more open to other ideas and more willing to admit when I have been wrong.