Who used the power of the state to persecute and kill the Donatists. Another Moral Relativist.
You don't know -- or more likely just don't care -- what you're talking about.
Augustine, of course, would not defend himself by saying it was okay for him or for that time or in his circumstances. He would say persecuting heretics is a moral obligation on all orthodox believers whenever we have the secular power to do it, and he would criticize us for laxity. He'd be wrong, but not a relativist.
When defending your position has you resorting to things like that, it's time to reconsider the position.