Yes, the vast majority of people doesn't behave like that.
Game theory is a discipline that studies the consequences of a even a small number of actors defecting norms that would otherwise be beneficial to everyone.
It's because of this subset that the world works the way it does. This subset is larger than you'd think and looking at countries beset with racial or ethnic or religious strife, it seems to me that nearly everybody has the potential for it. You are fortunate to likely live in a country where your existence isn't dependent on limited resources which have to be defended, so you can easily say "well, not everybody fights over resources or because they hate each other".
Game theory is a discipline that studies the consequences of a even a small number of actors defecting norms that would otherwise be beneficial to everyone.