For Evangelical/Fundamentalist Protestants, what is the motivation for supporting morality-based legislation?

Just to be clear, I'm only referring to activities that are victimless, or at least harm nobody except for those who willingly participate. If I understand Calvinist (TULIP) theology correctly, criminalizing something perceived to be a sin won't save anyone because refraining from that sin isn't enough to avoid hell. On the other hand, for someone who has already been born again, it is impossible to lose their salvation no matter what sin they commit. I don't mean to start a debate; I just want to gain some perspective.