By 2003, not a single major national law firm supported the Texas sodomy law before the Supreme Court, yet there were constitutionally defensible arguments to be made even in the case of that very nasty law. This was not an abandonment by those firms or prominent lawyers of a legal duty to defend an unpopular cause or client. One difference between the K&S case and Lawrence is that K&S actually undertook the representation for about a week. It's hard for me to work up much dudgeon about that based on harm to the client (the House) or to the zealous defense of its cause (DOMA). Another difference is the potential of blacklisting K&S, and the possibility that fear of such blacklisting, rather than an awakening to the firm's own principles and priorities, is really what drove the decision. I suppose this would have been the case with a firm that considered defending the Texas Homosexual Conduct law, too.