Furthermore, entire social theories are built on the idea that selfishness is the driving force behind all human behavior. I could quote Nietzsche or Schopenhauer, but there are also contemporary examples (Dawkins and Singer, to name a few). I don't know if I agree with them or not, but there's plenty of conceptual drilling to do before dismissing them as "sociopaths."
There'd be no society, institutions, states, healthcare, education, families and friendships without cooperation.