i used to think people were inherently capable of more good than they are. some recent experiences brought this to mind. i no longer believe in altruism. i think at some level, it all comes from a sense of self... some selfish notion is at play.
this isn't inherently evil nor is it inherently good. however, it usually leads to bad and if unchecked, even the seemingly good acts are bad.
does this come from original sin? no. it's how we're built. for every action there is an equal and opposite reaction. so if God created and claimed creation was good, then there was an opposite reaction which was evil. or think of it this way, a big light casts a big shadow. same with humans, we are beings of light and shadow, it's just easier to cultivate the shadow side.
i think a big mistake would be to deny the inherent evil that exists in humans but it's also another mistake to say the inherent good is not there either. people put bullets into other humans and they also jump in front of bullets for one another too. to say that this is because someone ate a fruit or talked to a snake is craziness. it's a mistake to think about why there is evil in the world or that there ever was a perfect earth. there is and has always been suffering. it's how you respond to it that counts.