Of course people will cooperate: it's in their self-interest. It's rational to recognize positive-sum situations and cooperate.

It's also rational and serves your self-interest to act "altruistically", as your empathy is a basic biological instinct that you can't really fight against, just like hunger or sexual desire. But just like with hunger or sexual desire, letting a biological instinct dominate your whole life is unhealthy and, tbh, pretty stupid.