Culture is tremendously important.
And it's not a contradiction for libertarians to advocate for a particular kind of culture which they (and I) might believe is more conducive to a free society (or to advocate against a particular kind of culture which might threaten the survival of individual rights). That's your 'some reason' for libertarian participation in the culture war---the belief that, with respect to liberty, some kinds of culture are invigorating and others are corrosive---and we (libertarians) don't come down uniformly on the left or right, or even uniformly with each other.
I do so all the time, and as long as I'm not employing violence in my advocacy, I don't see a conflict with my moral and political principles.
In the context of being in college, the fee is usually either mandatory or required to participate in any activity at all, whether it's the bible study that reserves rooms and gets no money from student government, the film series that spends like mad bringing in 35mm and 70mm prints, or something in between. At best, that's an extremely poor gradient of control over your own money and a consequence of centralizing control of funds in a way that many libertarians would likely oppose.