In that scenario, the guy who kills a family is also an executioner. But in the context of a world where 2% of the population is executed every year, presumably that is one without much of a justice system, and more of a dictatorship (where the dictator and their underlings are pretty aggressive).
Edit: I think "most aggressive and independently-minded individuals" needs to be defined further, because, obviously, a human without a tribe isn't going to survive long, but also no tribe wants an unpredictable wildcard. So one can be aggressive, with long term strategic thinking, but also not impulsive so as to become persona non grata.
An aggressive, long term thinking individual (or group) can cull other "aggressive and independently-minded individuals" so they don't develop into threats.
> the guy who kills a family is also an executioner
Quite literally not... "executioner: an official who effects a sentence of capital punishment on a condemned person". An executioner is someone who is legally allowed to give death as a consequence of a judicial decision, not simply someone who kills.
Words have meaning an homicide isn't a murder, a murder isn't an execution, &c.
Edit: I think "most aggressive and independently-minded individuals" needs to be defined further, because, obviously, a human without a tribe isn't going to survive long, but also no tribe wants an unpredictable wildcard. So one can be aggressive, with long term strategic thinking, but also not impulsive so as to become persona non grata.
An aggressive, long term thinking individual (or group) can cull other "aggressive and independently-minded individuals" so they don't develop into threats.