I think it's human nature to more vigorously defend your viewpoint if A: You feel would be strongly effected if it turned out to be false and B: You are somewha

I think it's human nature to more vigorously defend your viewpoint if A: You feel would be strongly effected if it turned out to be false and B: You are somewhat unsure of the validity of your claim. To me, this explains at least partially why the college age is one where you see this sort of strong rejection of anyone who disagrees. Many college students will have only recently laid any real claim to their own fully formed world view, and they don't have very much personal experience to back it up. Their world view also tends to be very wrapped up in self identity. All in all, I think this leads to a more vigorous rejection of differing opinions in some cases.