Ignoring that reality, and why 12 year olds are more likely to pick up a machete than a 30 year old, is what's bizarre.
Recruitment of child soldiers usually involves drugging the targets. 12 year olds are probably less susceptible to be able to realize that they're being drugged and to have the mental fortitude to retain their self through the grooming process. I suspect that even when drugged, a 30 year old will have a better sense of being drugged and is less likely to be brainwashed. There are also other shock-inducing factors that have a greater dislocating impact on 12 year olds, such as killing their parents (both it happening in front of them, and/or in some cases, them being forced to do it as part of the indoctrination process). I suspect that a 30 year old would be more likely to channel their anger at the "recruiter" than a 12 year old would.
Also kids are easily guided to do just about anything. They're easily impressed and even the brightest lack the experience to temper their judgement of what is a good idea versus what isn't.
Are there any sources, papers or studies indicating whether it is learned, innate or both?
Sources and empiricism are what we should be resorting to, not down-votes.
I want to know why the people going back and forth think one way or the other. If I rely on my own research I might not get the nuance that a psychologist or other person with a vested interest would be able to share.
There seems a great deal smoke but no light in this discussion. This is uncommon here on hacker news, normally sources are appreciated and I frequently see them brought in well before an argument begins, even on extremely casual topics. They often earn an few upvotes too.
So again, if you want to add to the discussion, add to it, don't try to control it.
At the moment there is no reason to believe either side and plenty of reasons to dismiss both, not as cranks, but at least as cranky.
Complaining on a form inherently lowers it's quality. As a rule Down-vote, Flag, or say nothing don't clutter up HN with posts that make for poor reading.
And yes, mass downvoting both sides of a thread is often better than getting in the middle of a heated debate.
Lets not pretend that it is.
As well as dogs. Dogs have empathy, even for humans.
So yeah, the idea that an 18 year old is struggling with an emotion that babies and dogs don't have much trouble with is a silly proclamation IMO.
Most of the reading I've done seems to suggest that that's something that's developed at a very young age, and very sensitive to early childhood environment, rather something people are born with.
There's a reason that everyone, for better or worse, wants to get to kids early, and often. Advertisers, religions, people trying to teach kids how to deal with advertisers and religions, militaries, etc... all see the value in "getting them young."
18-year-olds have been volunteer recruited and drafted for perhaps the entire history of organized armies. Child soldiers also have (and in some countries still are) enlisted also. I suspect this is only out of extreme necessity, as the moral and practical drawbacks are overwhelming.
When the United States has instituted the draft, it has encompassed 18-to-45 year-olds for immediate enlistment. 18-25 year-olds comprise the largest age group of new volunteer enlistees in the US. The largest barriers to military service qualification are health reasons and family situations. It would follow that younger enlistees would have lower likelihood of physical injuries and being the sole caretaker of a dependent.
Your post made sense until your bizarre digression to armed service being linked to incomplete prefrontal cortex development. It can be appealing to find sinister motivations behind institutions you dislike, but there isn't a basis in fact here. The explanation is tradition, health, and lack of obligations.