I can think of a few possible explanations:
1) I am actually a superbly effective and open-minded professor, who does nothing but expose my students to the world of ideas and encourage them to critically pursue what they think to be best--and a bunch of them have just happened to decide that libertarianism is what's best.
I'd actually love to believe this is true, but it's kind of conceited, and not particularly entertaining to contemplate. (Not the least reason being that I can't convince myself that the final clause there is at all accurate.)
2) I actually do attempt to indoctrinate my students, and really do put my opinions forward as the obvious truth, but I'm such a lousy teacher and clumsy indoctrinator that most of my attempts at brainwashing have completely backfired.
Related to this would be:
3) I actually do attempt to indoctrinate my students, and I'm relatively good at it, yet what I'm trying to instill in their brains is so obviously convoluted, wishy-washy, and ultimately incoherent that they wish, in response, to embrace the most streamlined and direct ideology around.
This explanation has the advantage of being compatible with a large percentage of all the commentary I've ever received from friends and online interlocutors about my politics, as pretty much every one of the 27 or so people who have ever unfortunately exposed themselves to my rants over the years can confirm.
4) What am I surprised about anyway? Opposition to government programs in America today has never been higher; nearly a quarter of the American people consider themselves libertarian in one sense or another; it's practically a "libertarian moment" out there right now. So what's the big deal?
I don't know if I find this explanation comforting or not, but I do find it the most intriguing. I'm teaching students about politics and government and law at a moment when the basic legitimacy of each and every one of them is being challenged (often lazily and ignorantly, it is true, but still, sincerely) as broadly as ever before in my lifetime. So perhaps I should see it as something of a triumph that a fair number of genuinely smart and committed students that I've been able to teach have taken some of what I've opened up to them and found within it a cause to engage matters of public life, rather than simply disengage in boredom and disgust. (Though there are many who do that too.) I suppose it's that sort of reasoning which lead me--when my students had done the work and came to me with their proposal--to agree to serve as the faculty sponsor (meaning: I'm the one who signs the bureaucratic forms) for their local YAL chapter. Sure, I'd kind of rather it be it be a chapter of the Young Democratic Socialists or the Greens, but at least they're not withdrawing: rather, they're making arguments, and that's something I can respect, and want to encourage.
Besides, I've discovered in talking often with my libertarian students--as they good-naturedly push back against my asking them to read John Maynard Keynes or Bill McKibben in the classroom--that the libertarianism and constitutionalism which animates many of them isn't just a chip off the Koch Brothers' block. Their deep suspicion of government systems extends to corporate and religious systems as well; many of them reject a bottom-line individualism with its obsession with rights, and instead identify with what might be called a kind of Tocquevillian localist promise: that as communities and families, as well as individuals, they'll someday be free to govern themselves, and build something themselves, and judge the morality of something for themselves, without getting dragged into (in their view) endless and corrupting fights over whether to allow this tax break or violate that social taboo. If you dig into the data behind the aforementioned studies, that ambivalence is evident. And even more appealing to me, given my own political preferences, is that these evolving libertarian ideas, by developing at least partly outside the paradigm of inviolable property rights and such, may ultimately produce the kind of thinking which can contribute to what I see as truly positive egalitarian or anarchic developments, whether they be some kind of "bleeding heart libertarianism" or good old-fashioned economic mutualism. That may be too much to hope for--but then again, the notion that the present generation is going to give rise to a more affirmative, aggressive, but also decentralized left has at least a little grounding in recent political developments:
[A] mountain of survey data--including the heavily Democratic tilt of Millennials in every national election in which they have voted--suggests that they are not especially susceptible to the right-wing populist appeals....[T]oday, a Republican seeking to divert Millennial frustrations in a conservative cultural direction must reckon with the fact that Millennials are dramatically more liberal than the elderly and substantially more liberal than the Reagan-Clinton generation on every major culture war issue except abortion....They are also more dovish on foreign policy. According to the Pew Research Center, Millennials are close to half as likely as the Reagan-Clinton generation to accept sacrificing civil liberties in the fight against terrorism and much less likely to say the best way to fight terrorism is through military force....Millennials show a libertarian instinct in the privatization of Social Security, which they disproportionately favor....But Millennials are also more willing than their elders to challenge cherished American myths about capitalism and class. According to a 2011 Pew study, Americans under 30 are the only segment of the population to describe themselves as “have nots” rather than “haves.” They are far more likely than older Americans to say that business enjoys more control over their lives than government. And unlike older Americans, who favor capitalism over socialism by roughly 25 points, Millennials, narrowly, favor socialism.