I heard the same process has been running on humans for the last few millennia. Apparently 2% of the population was executed every year, wherein presumably the most aggressive and independently-minded individuals are overrepresented.
I look at aggression as an emotional state, rather than the capacity for violence. Consider the army. Soldiers are expected to commit violent acts on enemy soldiers, yet they are also expected to maintain emotional control. They are typically expected to avoid killing civilians. They are certainly expected to avoid killing friendly targets. Clearly they have a capacity to commit violence and I suppose most people would say there is a need for aggression because of that. On the other hand, they are not aggressive in the sense of random acts of violence (as would be the case of a bear or a raccoon attacking a bystander).
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.
Even in warring countries, or countries without much rule of law, death rates (from all causes) is ~1.1%. Let's say good data is not available, and the real figure is double or triple that number.
An annual death rate of 2% just from executions would be in a society with a super aggressive dictator (or faction, I guess).
For more context, annual WW2 death rates over 5 or 6 years were not as high as 2% per year. Only Poland seems to have been higher.
Something something autodomestication...