When I was a kid, adults would always say that bad kids grow up and learn to be better. First problem with that is, why do bad kids get a pass for being bad so easily? Good kids and bad kids who "learn" one day become equals even though the good kid never hurt anybody before? And then, do bad kids really grow up?
I'm not talking about kids who make mistakes... honest mistakes... and who learn and mature and apologize when necessary. I'm talking about kids who hurt on purpose, knowing they are hurting others, and knowing they don't like to be hurt themselves. I don't think those kids do grow up... they just learn they can get away with it.
So, I'm not sure most people are good. I'm willing to concede good people exist. I'm just not that sure society rewards good people so they flourish. And then there are some good people who become so frustrated that they just decide to start being bad because it doesn't matter. Life can ruin good people who are constantly shit on... and that is tragic, but now they are bad people too.
IF society and evolution encouraged good over bad, then bad would be a rarity and most people would be happy and helpful to others. The fact that is not the case, means inherently that we are not good, because we designed a society that doesn't reward and encourage good behavior on average.