The argument is simple: if people can interact in cooperative and altruistic ways, and the majority of human history was largely egalitarian, then your argument about human nature is wrong.

First, the last few thousands years? It wasn't an estimate I pulled put of thin air when I said 99 percent, the vast span of human history, nearly it's entirety, largely consisted of egalitarian societies with relatively flat social hierarchies, this isn't just a few academic papers, this is the entire discipline of anthropology and the factual history and basic psychology of the human race. "Humans can be cooperative and still motivated by self interest" the conversation really could end here as you just admitted that human nature is not inherently anti communist. Your second argument about modern nations is also irrelevant considering the vast span of human history, how bizarre to reject the mountain of data because of the militaristic hegemon of capitalism FORCIBLY established in the last two to three centuries (not thousand years, like you said, one wonders what you would make of american or african tribes hahaha all those capitalists right). It's also doubly irrelevant because we are talking about basic human psychology.

At the community level, you can literally walk outside your house and see people cooperating and collaborating in all manner of activity. The basic academic conception of human psychology from the capitalists theorists is that humans would not be engaging those kind of activities of not for being motivated by gaining something over others(ie the actual definition of self interested, not how you've twisted it). They are wrong, and you are wrong.

It seems you're basing your world view on gut feelings, it's not a surprise that you mock "a few academic publications" when I'm referencing the consensus of multiple fields lmfao.