That's what Maggie Gallagher is arguing:
Kagan waded into the DOMA case, amending a brief that offered “responsible procreation” as a reason for DOMA to instead explicitly reject procreation and child wellbeing as a reason for defining marriage as one man and one woman undermining the law she claims to be defending. We’ve seen this tactic in state litigation before: Attorneys general pretend to defend the marriage law but sabotage the case by explicitly rejecting procreation as a reason for marriage. (See Jerry Brown in California.)
If you doubt my reading of Kagan’s record, see the Human Rights Campaign’s press release, which specifically cites her support for “marriage equality” in cases before the Supreme Court as a reason for voting for her. HRC and Maggie Gallagher agree: A vote for Elena Kagan is a vote for finding a constitutional right to gay marriage that will overturn marriage laws in every state.
Every state? And when you read HRC's statement, it says "issues related to marriage equality" not marriage equality itself. Althouse examines Kagan's record on the issue. I think she makes some fair points.