Every law is a legislation of someone's morality. It is called a Social Contract.
Also, Dems have been losing many elections, so they now complain about us "imposing" our morality on them. They didn't complain about this when they were winning. One other thought, since Dems often don't go to church, they don't see their own set of values or "morality" as really being a "morality." They see their values as just being common sense. They think that the only "morality" that is imposed is from the church-going conservatives. Dems don't see their secular humanism as being just as much a "religious" point of view as regular Christianity. That is why they think of themselves as being "neutral" and "moderate" and "tolerant", while all we Christians are biased and bigoted and religious. The bottom line: Dems reject God-based morality.