I kinda like the fact that he didn't hide himself. The whole public/private part was simply that he thought he was replying to an individual and not 'all muslims'. He has tenure so there isn't anything they can do to him. its about time a non-commie professor uses tenure to say some incredibly unpopular things on a college campus. Typically, its some nutbag prof. explaining that Rummy and Cheney were behind 9/11 or that the people who died at the WTC were 'little eichmanns'.
I may be mistaken, but the protection of tenure usually applies to research and teaching. Prof. Wichman's letter has nothing to do with Mechanical Engineering. Most leftist professors, however, are in the Humanities and Social Sciences, where politics, research, and teaching are not so clearly separated.