It's more complicated than "people are inherently asshole" or "people are inherently monster". Baby don't have the brainpower to understand something like "if I help other, other will help me in the future and everyone doing so on a society scale means we'll have a prosperous society, so being a good person is obviously the right way to live", baby/kid only understand "need/want = take". But if you don't correct that behaviour in a baby, then they'll grow up as adult that will have learned that "want = take" is a great way to live and that's how they'll live their life. If kid would grow up good person no matter what, they all the spoiled kid from parent who grew without ever lacking anything would turn out as wonderful people, I don't think I have to explain that's not the situation.
Then there's the problem that someone asshole behavior is someone else benevolent action. Some people truly believe that the best thing people can do is pray to the specific god they believe in, for them prayer is an absolute good no matter what. In a position of power, these people would gladly brainwash and/or force people to pray to their particular god, they'd even accept some lesser evil (say killing a few dissenter) because of the incredible good of prayer, in the same way that someone else would be okay with stealing bread to feed a starving family. There's no universal good that kid will naturally grow up into, even things that you would thing would be deeply rooted in every human can be countered. You'd think everyone would follow "pain = bad" to the absolute letter, but plenty of people enjoy some form of pain or another, from BDSM amateur to extreme sport to people who recreate religious scene (iirc there's a few place in the world that genuinely have people get crucified, minus the dying, to celebrate Jesus).
A system can only succeed if it as safeguard against any individual gaining too much power, because if even if it means that good people will be hambered, it's far more important to prevent bad people from becoming all powerful, especially when there's no universal definition of bad (ie, killing is bad, but I think we can all agree it's a pretty good thing that Zelnesky and the Ukranian aren't all absolute pacifist who refuse to kill). Capitalism does a bad job of this, but it's still far better at it than literally any other political/economical system that have ever been tried.