This statement is right on, and I'm not a libertarian:
Asking a Christian to actively participate in a same-sex wedding is simply the equivalent of inviting a follower of Hinduism, Zoroastrianism, or any other faith to participate in an altered version of a ritual central to their religion.
Granted, some Hindus and Zoroastrians might like to participate in the altered ritual. But what would you say about someone who wished to force them to do so against their will?
You would probably call them a spiteful totalitarian who maliciously delights in imposing themselves on others. And you would be correct.
See also: Update 2: Arizona SB 1062