Fred Phelps is an example of the most extreme. Others like Jerry Fawell, Pat Robertson, James Dobson, are the ones who seem to be the major players in promoting Christian Supremicism.
Same sex marriage's main (and possibly only) opponent comes from Christian Supremacists.
Unless, or until you add the Pope and Gordon B. Hinckley in there it does not wash. The major opposistion in California and in other places comes from the Roman Catholic Church and the Church of Jesus Christ (Latter Day Saints).
And if you want to read the real deal, not the clown car stuff like Phelps - who even the people on his side seem to hate as being nothing more than an attention whore - Fallwell is pretty much retired, Robinson is content making money off his network, its the new people that are running this show, and they are much more dangerous then the grandstanders that came before. Check out the church that Sara Palin belongs to, or look up 'quiverfull movement', or 'Dominionism', or 'Christian Reconstructionism' and find out what these people are really thinking, and where they want to go.
There is a site called Theocracy Watch which is a pretty good starting point, and has a lot of the basic stuff well laid out.
Moreover, what exactly are you doing about it? I think that the following section is basically correct, and if so, preventing this is a job for all of us.
All radical movements need a crisis or a prolonged period of instability to achieve power. And we are not in a period of crisis now. But another catastrophic terrorist attack on American soil, a series of huge environmental disasters or an economic meltdown will hand to these radicals the opening they seek. Manipulating our fear and anxiety, promising to make us safe and secure, giving us the assurance that they can vanquish the forces that mean to do us harm, these radicals, many of whom have achieved powerful positions in the Executive and legislative branches of government, as well as the military {ed note. The Air Force in particular}, will ask us only to surrender our rights, to pass them the unlimited power they need to battle the forces of darkness.
They will have behind them tens of millions of angry, disenfranchised Americans longing for revenge and yearning for a mythical utopia, Americans who embraced a theology of despair because we offered them nothing else.
Moreover, they are not afraid to get out, to be seen and to be identified with the movement, something we have a very real problem with.