"But," Robert counters, looking a little more serious about this, "I perform human instinctually-based acts on you, and that is not a problem to you... or so it seems. So... why would it be one in the opposite situation?"

Not that Robert is good at separating his instincts from his cognitive functions, for multiple reasons, but he is certain that this is true. And if Don puts up with it from him, then there's literally no excuse about the opposite.