Such an opinion by Chief Justice Roberts would not only strengthen the decision but put into the Supreme Court's toolbox the importance of viewing discrimination against someone on the basis of her sexual orientation as simple sex discrimination. This would help bring "heightened scrutiny" into consideration in future gay-rights cases.
Heterosexual marriages do not automatically lead to happy households and well-balanced children. Parents are parents -- and all can make bad decisions, learn as they go, or not be perfect. It doesn't matter if they are gay, straight, single or otherwise. But to deny protections to parents already raising children isn't right, and the only purpose it serves is to hurt those children.