Tenure is a special thing for everyone involved in academics. It’s a reminder of the power and importance of the role of professors and teachers in society, and of the traditions that uphold that role.
But what’s not reasonable is to try to protect tenure by keeping people out arbitrarily, by denying tenure for political reasons. As a strategy it’s great and perfectly understandable — but it also undercuts the very reasons tenure is important.
Tenure is designed to protect people from recriminations for saying unpopular things. As a society, we benefit from a wide and diverse range of opinions, but that doesn’t mean that we, as individuals, want to hear these diverse opinions. So it’s natural to use intimidation to try to shut down dissenting voices, starting with the loudest. Academics, for a variety of structural reasons, often have political agendas, loud voices, and usually work on the public dime — and so make excellent targets for intimidation. The purpose of tenure is to protect those academics who have shown themselves to be responsible from this outside intimidation.
Trying to deny conservatives and Intelligent Design advocates tenure is just a form of preemptive intimidation aimed at junior researchers and teachers. But tenure doesn’t just exist to protect a single, unitary political class — college professors — from external threats like the boneheaded Horowitz. It also exists to protect diversity within the set of professors. The discipline of economics benefits from having a wide range of positions, because internal debate — much like competition in markets — is the best way to find good answers to economic questions. The same is true in biology, in sociology, in philosophy. The same ought to be true English, in Women’s Studies, in Science and Technology Studies.
So to deny a good researcher tenure because they have outré, or even wrong, beliefs — when that researcher has proven to be capable and responsible in their main area of expertise — is to damage the very methods we use to gain knowledge and learn true (or mostly true, or truth-like) things.
I also think the fastest way to refute Intelligent Design — is to take it seriously. The IDers can ignore scientific refutations of ID because they are mostly located outside of real scientific practice — and they are forced there by shenanigans like this.