I don't even know where to begin on this one. A system which criminalizes mortal sins, to be defined by the legislature, would give them extraordinary power and greatly diminish the liberty of citizens. Laws would be arbitrary and would invade almost every aspect of a person's life. The rule of law would vanish, to be replaced by the rule of the majority. Individual rights would be non-existent.
This is totalitarianism. I can see little difference between this system and that of the Taliban, except perhaps for the punishments imposed on "criminals".