Is there any proof that humans are born into sin?...

[OnlyNatural]

I don't personally think that we are, but there are a lot of Christians who point to the fact that kids have to be trained not to be selfish, as one example, that we are all born into sin.

We are all self-interested, especially as children, but this doesn't mean we don't care about anyone else, or that we're bad people. Children also spontaneously show empathy, and can recognize that certain behaviours (like hitting others) are wrong.

To say that humans are inherently good or inherently sinful is a huge oversimplification of human nature, though. It also ignores the incredible importance of upbringing and environment in shaping one's character.

The idea of original sin is just another way to control the faithful. Religion poisons us, and then tells us the only antidote is to surrender ourselves to God's will.