After reading the text (courtesy of the Wall Street Journal) of John McCain's speech to the graduates of the New School, I disagree with Professor Althouse's take on his speech. I don't believe the speech was inappropriate for a graduation, being about the need for civil debate and for reconciliation. As far as his delivery of it, I can't say without actually hearing it. I'm not all that sure I'll get an objective account from someone who blogs for the Nation, given that magazine's political slant. I suspect that a different view of his speech would be expressed at National Review, for example.
Was he "asking for it" by speaking in front of a so-called liberal crowd (so-called because they definitely failed to behave in a way consistent with "liberal" values)? Yes, speaking in front of a crowd that disagrees with you tends to encourage hecklers. On the other hand, if the Senator only spoke to friendly crowds, the same people who would turn their backs on him during his speech would accuse him of being afraid to speak to those who disagree. He just can't win.
Not that it really matters all that much. The boorish, rude, and insulting behavior of the students and faculty of the New School who condemn someone for giving a speech to a group they dislike tells me that the actual content of Senator McCain's speech was irrelevant. Their minds were closed long before he opened his mouth to speak.