Should We Have an "Irrational Animus" Constitutional Doctrine?

To me, the constitutional question raised by Limon and other gay-rights cases (Romer, Lawrence) is whether we should have a doctrine that some laws should be struck down because they reflect an "irrational animus" toward the person even though some non-hateful reason for disfavoring the conduct could be articulated (even if that reason is unconvincing, overinclusive/underinclusive, etc.).

In Limon, the other reasons seem to me very unconvincing (e.g. if the concern is with physically high-risk anal sex, then criminalize that), and when combined with the possible severity of the differential criminal penalty, make a strong case for finding animus toward the persons as opposed to concerns about the conduct.  What's wrong with having an equal protection doctrine that invalidates such a law?

The constitutional worry on the other side, at least for me, is what such a doctrine potentially opens the door for courts to do.  After all, the Massachusetts Supreme Judicial Court in Goodridge used this same analysis to declare opposite-sex marriage laws a product of irrational animus, which seems to me a tremendous case of judicial arrogance and overreaching (although I have some sympathy to a state that tries out same-sex marriage as a policy idea).  Michael, maybe I should be aware of your answer to this question already ... but do you think that Goodridge as a constitutional matter was a case of judicial overreaching?  Are there reasons to have confidence that once courts recognize a doctrine of "irrational animus," it won't mushroom in that sort of way?  If there are reasons to think courts will stop at the egregious cases, then I'd be go along quite happily as a doctrinal matter with decisions striking down a law like the Kansas one.

Tom