T-Rex: Is there any motivation that can't be reduced to self-interest? Absolutely! For example, I might give to charity: charity is the opposite of greed!
God: MAYBE YOU'RE JUST DOING THAT TO FEEL BETTER ABOUT YOURSELF
T-Rex: Dang!
T-Rex: And if I do it anonymously, that still lets ME feel good about myself. Alright, what if I rescue someone from drowning? And I hate the person, so I don't feel good about saving them!
Dromiceiomimus: But others will still know you saved someone, hero, and you might reason that saving this jerk will make them less jerky to you: self-interest again.
T-Rex: DAAAANG!!
T-Rex: Darn it! Is everything we do ultimately reduced to greed?
Utahraptor: What about LOVE?
T-Rex: No go: you expect it to make you feel good, so you could be doing it out of SECRET GREED. What if you and I are the last people left, and I give you a real nice cookie WHILE SIMULTANEOUSLY cutting off my own head with giant scissors? That's kindness without good things coming to me, therefore there's no self-interest!
Off panel: Well, I'd enjoy the cookie and remember you fondly, so there's still self-benefit. Really, all you've done is found a way to escape a hellish post-apocalyptic environment through baking.
T-Rex: My friend, I believe that counts for something!!
