Why is it wrong to take advantage of other peopls's stupidity, naivety?

A psychopath would see you as a tool to be used and generally believes if you can be manipulated then you should, because that's your fault (not theirs) and they will use you to get what they want - even if it's you they want.

It's interesting that both the psychopath and the sane person can look at this statement as having an element of truth in it. Whereas it'd be nice not to have any psychopaths so we can avoid their potential manipulation, it would also be equally viable to be individual and strong enough not to be manipulated so naively. The former is impossible and the latter isn't, hence an admitting to yourself now before the fact inoculates you to a fair portion of any potential occurrence.

The broader question of whether it's wrong to take advantage of other people's stupidity or naivety is complicated. On one hand it feels wrong when we see this happen - but I feel that that sense of wrongness is heightened when the difference between the manipulator and manipulated is very large (think parent & child manipulation). That being said if the gap of equality in competition is close then it's almost like a stand in for an assessment of ability (so is a type of game) - a good example is professional fighting where you're always going to have to take advantage of someone's errors (stupidity) and you can induce more errors by feinting and conditioning (naivety). In other words, anything you can assume yourself being taken advantage over is worth you safeguarding yourself against it by a conscious effort to admit you could and so you won't.

Thinking you won't or don't is stupid and naive.

/r/JordanPeterson Thread