From the dissent read by the Chief, here is the money paragraph for the anti-gay politicians, on which they will hammer over and over:

Understand well what this dissent is about: It is not
about whether, in my judgment, the institution of marriage
should be changed to include same-sex couples. It is
instead about whether, in our democratic republic, that
decision should rest with the people acting through their
elected representatives, or with five lawyers who happen
to hold commissions authorizing them to resolve legal
disputes according to law. The Constitution leaves no
doubt about the answer.

This will be the argument (for the ones who want to look educated and try to defend their position, rather than just ranting) used behind TYRANTS IN BLACK ROBES exclamations.