Santorum was confusing personal activities of a private nature with legal activities of a public nature.

Santorum was talking about the Texas anti-sodomy statute, not any gay marriage statute in any state, but he nevertheless equated dating behaviors with the legal structure of marriage. For a US Senator to get legal institutions confused with personal, private behavior is quite troubling. This tells me that his personal beliefs are interfering with his ability to discern the essence of a legal argument. But he's my Senator, so I knew that already.

Re: your definition of the liberal viewpoint (which is defined for conservative sensibilities rather than for accuracy), a more precise expression of the liberal viewpoint is commonly ascribed to Voltaire: "I disapprove of what you say, but I will defend to the death your right to say it."

If radicals on the left believe (as you say) that anything goes except what they don't agree with, the equal and opposite radicals on the right believe that nothing goes except what they do agree with. Cf. Senator Santorum.

And so is equilibrium maintained.

Regards--
Mary Anne