I call my own view "enlightened self-interest". I don't really believe in altruism. Simply put, people behave better when you treat them well, than when you treat them poorly.

Treat people well, and you get Scandinavia; a peaceful, stable place with widespread prosperity, low crime, low violence. Treat people badly, and you get Somalia, Afghanistan, North Korea. Which place would you rather live?

Also, helping others just plain feels good. Especially seeing that you've changed someone's life for the better, and you get to see that smile and joy and know it's because of you. Why does it feel good? Because it's our strongest survival trait. Our ability to cooperate for mutual benefit, to care about each other, is our single biggest strength as a species--not our opposable thumbs or our big brains. It's why humans are social, and why language exists. Language helps us help each other. "Oh, don't eat that. It's poisonous". Helping us cooperate for mutual benefit is why big brains exist.

Our ability to cooperate for mutual benefit is what makes civilization possible at all.

And lack of compassion is what underlies most of the social problems we're having right now; rape, abuse, depression, corruption, addictions, homelessness, crime, violence, suicide.

True, there are always those who try to cheat the system. But that behavior is both destructive and self-destructive. Cheating is widespread in Somalia. As a result, they are impoverished, full of violence, even the rich have to live in fortified guarded prison-like compounds out of fear, and militarily very weak.

A happier world makes my own life better. Making the people around me happier, makes me happier. It's also where that feeling of inner fulfillment with life comes from.