The subject is actually interlinked with a number of important ones - capital punishment, war, laws - so indeed I take it seriously.

To be clear, it is the bulk of Christians that “narrow the relevance of Jesus' teaching”, not me, not the Catholic Church.

We can expound on why at length after you take a look at the hypothetical.

The short answer is that it became clear when the Church dealt with Judaizers that the entire Old Testament laws did not transport into Christianity, and that Jesus was silent on a large number of moral issues, fornication being a good example.

The answer was that the cultic (e.g., kosher and Temple sacrifice) laws were voided, but the entire moral law remained, including the Natural Law. Jesus was silent about the role of the state, leaving the Natural Law in place.

To take your position would demolish the state, which would be unable to pass and enforce laws, form armed forces and defend itself, conscript citizens, and so on. Evil would march the earth.