Man is a wolf to another man. Homo homini lupus. Thomas Hobbes said that in part of his explanation about realism, a perspective that views states' behavior as self-centered, because that is human instinct. (sorry, this is so IR-ish.)
I really can't blame realists for attributing self interests to humanity. It's true; (most) people focus on themselves rather than their surroundings. Regards to others' wellbeing mostly come secondary.
Allow me to tell you what I encountered in Nabawi Mosque, Medina. There resides Prophet Mohammad's final resting place, and the area around it is called the Raudha (not sure if I spelled it right), where prayers are most likely to be listened.
We have to wait hours to get in, because it is a small space and eeeeveryoneeee wants to get in. The Askaris are shouting here and there to calm people down, telling them to wait. Just like International Law to states, the Askaris aren't always listened. Who cares if I step on an elderly as long as I get to enter the holy site, right? Who cares about those tiny Indonesians when I have this bigger body to push them off? Who the heck cares about the Askari screaming at us to queue in order if I can just push past the crowd? Yay, I get to pray on The Prophet's cemetery!
Wow, on the second thought, that was quite rude and generalizing of me. I apologize. It was an unfair description, I was annoyed. In fact, not everyone behaved like that. Many are nice and considerate. And about the people who are not, I guess there are justifications: they might have waited years for a chance to be in this holy city, and all they want was to pray near the Holy Prophet's cemetery. I can relate, the strength of faith and hope is indeed powerful.
So. Realism is still not wrong, but it is not quite right to say that humans are inherently selfish without looking at their backgrounds. One does not simply generalize human behaviors. I still regard realism as the most convincing IR perspective so far, though.