Belief is the key word in that.

Others believe people are inherently good, and it’s society, culture, or poor upbringing that corrupts. I’d personally lean in that direction, though leave belief out of the equation.

And yeah, idealisms nearly always fail to live up to intentions, if for no other reason than they’re based on belief rather than consciousness - distorted maps of the territory full of assumptions and biases rather than a clear vision of the territority, objective honesty, and consciously-directed wisdom of how to harmonize with natural law...