Getting into the mind of a psychopath

[ApeNotKillApe]

I imagine it's a much more efficient existence in a lot of ways; a high-functioning psychopath can thrive in the human environment, selection works in their favour.

Obviously not. One or two may thrive but if selection really worked in their favor we would all be sociopaths by now. We are a social species and as such required to work together and not in the sense of using and abusing each others. Our societies would crumble if that was the norm.

And it's important that in the overwhelming majority, psychopaths are made by childhood influences and aren't born that way.

Humans are a very new species, their social order has altered radically over a very short period of time. Civilization has created a new type of environment with its own selective pressures, where humans largely struggle against each other, even within their own communities.
The typical characteristics of psychopaths - manipulative, ruthless, charming, cunning, egotistical/narcissistic, are potentially very advantageous traits in many aspects of human society throughout the last few thousand years if not before. A lot of psychopaths are bankers and lawyers and politicians, the personality type gravitates towards positions of power, and is equipped with a very useful set of traits for achieving them. That seems to me like an example of a species thriving in an ecosystem.