In a republican form of government such as ours, We the People, via our representatives, most certainly have the legitimate power to regulate or even outlaw vice. And to do so is in no way a violation of the natural law.
I am NOT sure if a Republican form of government such as ours will always outlaw vice or even pass laws that encourage virtue.
John Adams once said: “Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.”
So, If by natural law, we mean the laws given to us by nature’s God, and if we believe this God gives us morality, then in a Republican form of government, it behooves the citizens to pass laws IN HARMONY with natural law.
Now, consider a state like NY or Colorado that passes a law FORCING business people to service gay weddings under penalty of stiff fines or perhaps even closure of businesses...
That is an example of a positive law that is a violation of natural law ( that is, if we agree that homosexuality is against natural law ).
Certainly, but doing so in the absence of a common consensus on just what constitutes vice will be ineffective and even counterproductive as it will breed contempt for the law, viz, laws against alcohol or marijuana consumption.