Oh yes, moral laws are superfluous, which is why both the OT and NT abound with them, and affirm civil authorities enforcing them. /sarc
Laws for morality do not change the heart.
They enable enforcement of justice and in some cases, where the death penalty is applied, yes, does cause a reduction in law breaking by reducing recidivism and maybe action as a deterrent for some kinds of crime.
But morality comes from within and cannot be legislated. Laws mostly enable the application of justice when they are broken.