Ruth Marcus, who opposes DOMA, writes in the Washington Post that she opposes HRC's intimidation tactics more:

It’s easy to beat up on a big corporate law firm for acting cravenly in its financial self-interest. In the case of King & Spalding, the Atlanta firm that abruptly reneged on its commitment to defend the Defense of Marriage Act, the pummeling is entirely deserved. But the bigger culprit is the Human Rights Campaign, the gay rights group that orchestrated the ugly pressure tactics against King & Spalding.

... strong-arming the lawyer to drop or avoid the unpopular client is not an acceptable tactic. This is not, or shouldn’t be, a left-right debate. It is true whether the lawyer is defending murderers on death row, Guantanamo detainees or a federal law — a law, it must be pointed out, that was passed by overwhelming congressional majorities and signed by a Democratic president.