[He holds up his hands as the universal sign of surrender.]
Hey, you don't need to convince me. But what we think really doesn't matter. [He's not saying that Robin won't consider everything they have to say on the subject --and from the sound of it, Zatanna has had more to say than he has-- but just that the decision is ultimately Rob's to make.]
Besides, is it really that big of a deal f he doesn't tell her?