From the LA Times staff opinion page:
This is civics book stuff [that all clients deserve representation], but it's controversial with some gay activists. Evan Wolfson of Freedom to Marry referred to Clement as a "hired gun," an appellation that can describe any lawyer who doesn't work pro bono. (If Clement defended DOMA out of conviction, he would be abused even more.)
The law firm's critics raised a side issue: that the House Republicans' contract with King & Spalding prohibited lawyers at the firm from commenting on DOMA. If that's the case, the firm overreached. But it beggars belief that it dropped this hot potato because of that provision rather than because of the efforts of Human Rights Campaign, the gay-rights organization, to "shame" the firm.