No one NEEDS not to be shouted down on campus. The issue is what is best for maximizing the free exchange of ideas, broadening horizens, and sharpening the mind.
Moreover, these speakers are being invited to campus by student groups that want to hear what the speaker has to say (whether or not they agree). If you have a school where student groups are allowed to invite speakers and the school provides facilities, then it is wrong to discriminate against those groups and speakers that are not on the left side of the political spectrum. What is the point of having groups inviting speakers if each side of the political aisle shouts down the other? Will anyone ever have their ideas challenged?