“There are certain laws which all peoples follow, peoples who have never had any contact whatsoever with one another. They have arrived at the same laws independently and therefore must have received them from a divine source.”
If you already believe in God, this is a persuasive argument; but it is flawed. It assumes as a premise that human beings must be either completely the same or completely different. For some reason it is unacceptable that they be the same in some ways but different in others, by their own nature and without divine intervention. Moreover sameness gets the preferred status. Why not argue that the laws which are different have come from a divine source, that God in his infinite wisdom guaranteed not our unity but our differentiation and separation?