That's kind of the idea. Psychopaths are parasitic by nature. They will live at the expense on others' well-being for their own. Natural selection isn't something that is produced. It is a process which states that a species either preserves its genetic content over time or doesn't. The "survival of the fittest" is the most common idea connected to evolution, but it isn't fully correct.
Just see how humans in different continents have preserved and fostered certain genetic traits, regardless of fighting. Saying that "natural selection is produced by selection by warfare in human societies" is completely unfounded and doesn't make sense.
Right and we have labs and genetic engineering, vaccines, antibiotics, etc. All of that has an effect on gene preservation. And then we have world wars where hundreds of millions die, with extermination camps, and genocides, some of which still are happening.
I would say we have no easy way to divorce social warfare from natural selection.