If the conservatives and the religious (some) are so against altering "traditional marriage" why aren't they leading the way when it comes to instituting civil unions or domestic partnerships?

All I hear is “we have no problem with gay people having unions, but we don’t want to change the definition of marriage”. Seems to me that if they really just wanted to preserve their idea of marriage, they would be trying to institute an alternative. This is why I believe gay marriage foes are truly just homophobes and bigots, who are more interested in being discriminatory than actually preserving some institution.