"Suppose for the sake of argument that Tony were not going to find out. Alternately, suppose he were not going to have trouble with it if he did. He won't have as much trouble with it as he would with your current choice of outlet, I can tell you that—the crucial distinction being that I know precisely what I am getting into."

Oddly enough, the disaster that was their last encounter is exactly what allows him to be so sure of this. He does know what he's getting into, and can therefore convince Tony to accept his decision.