That law was given by direct revelation to the Israeli theocracy, and yes it was the right thing to do under that jurisdiction, hard as that is for moderns to swallow. But the Church is a spiritual creation, not a physical nation, and as Jesus said, his kingdom is not of this world. This is the New Covenant, not the Old. We do NOT wield a sword against sinners for private sins, only against those who by their public wrongdoing make civil life impossible because they have wandered too far from the universals of natural law, i.e., law that everybody gets whether they believe the Bible or not, like laws against murder, theft, etc.
Peace,
SR
Who are you preaching to? I know the Bible - so, your discourse might be better served on someone unfamiliar with it.