Why do you assume that any laws passed to regulate morality would be malum prohibitum and not malem se?
Malum in se - is an innately immoral act, regardless of whether it is forbidden by law. Examples include perjury, theft, and murder, -- not motorcycle helmet 'laws', smoking bans, gun prohibitions, etc.
Regardless, while I tend to agree that malum prohibitum laws violate due process,
Tend?
they certainly seem popular with both the left and the right. From click-it-or-ticket, motorcycle helmet laws, smoking bans, and etc., they spawn like rabbits. I don't see many of them being overturned due to their debatable constitutionality.
So now you admit you find Malum Prohibitum - An act which supposedly is 'immoral' because it is decreed to be illegal; -- debatable.
Well, I don't agree. We've never given governments the power to decree what acts are to be immoral.
Common law has long established what are 'innately immoral acts', -- we don't need 'new' socialistic moral majorities dictating any more.