I fundamentally disagree. I don't go around treating people respectfully (as opposed to, kicking them or shooting them) because I fear consequences, or I expect some future profit ("iterated game"), or because of God's vengeance, or anything transactional.
I do it because it's the right thing to do. It's inside of me, how I'm built and/or brought up. And if you want "moral" justifications (argued by extremely smart philosophers over literally millennia) you can start with Kant's moral/categorical imperative, Gold/Silver rules, Aristotle's virtue (from Nicomachean Ethics) to name a few.