Most likely, it was thrown in in order to provide contrast to the Roman Regime that early Christianity was in opposition towards.
Also, I find it interesting that you are considering sins to exist for pragmatic reasons. Wouldn't most people who are religious contest that line of thinking, saying that sins exist for moral reasons, or because god said so? In my experience, people treat this as a matter of faith, and attempts to rationalize commandments are actually considered to be an attack upon faith.