You can argue that human cognition allows for the world we see around us, but that doesn't mean this was necessarily unavoidable, or that we're naturally selfish, or whatever else. It's also very self-defeating as an argument because we can point to countless examples of cooperation, both past and present, including people saving someone from drowning for no monetary gain. And I don't know you personally, but I try my best to be a good person out of love for humanity, rather than expecting a reward.

But let's say that it is human nature to be selfish. It's still a silly argument against socialism though, since we could still build systems that don't reward our worst Impulses, but rather function with checks and balances to prevent them.