I became more liberal in college, I studied engineering for bachelor's and master's. I didn't have this liberal/conservative indoctrination with my professors. I could only say my economics professor may have been conservative, but then he wasn't indoctrinating anyone, just as my other professors said nothing of politics, so I really can't say.
However, I still became more liberal. The environment of American universities is a place where you must learn to live with a lot of people that differ from you ethnically, religiously, racially, socially, etc. That's what dorms do, and thus people become more liberal. You can't compare American universities with Korean universities, the populations in Korean universities are nearly uniform, it's just a bad argument. I believe it is the diversity of the institution that definitely does a lot to foster the more liberal attitudes you see in colleges.
When I look at conservatives, I often see a group of people who think they know how to define others. They think they know. They'll say, "Gay people are this way...," and if they never have to see gay people, they'll probably continue to think that. A person in high school may think this way and then go to college where he/she will see more gay people and either become obstinate with his/her views, or have to adjust to the reality that gays are not the way he/she defined them, thus probably becoming more liberal. But that's just the way I've seen it.