Nothing is more important to me, or a greater source of joy, than my family, and I speak here for just about every liberal I know. Many of us who have come to support gay marriage see the conservative argument on its behalf as decisive: If we believe in fidelity and commitment, shouldn't marriage, the institution that promotes both, be open to us all? Moreover, as a policy matter, I share the view of my conservative friends that the breakdown of the family is a social problem that both left and right should care about. This is an issue on which we need to seek common ground, not provoke deeper division.