Maybe humanity is not as 'humane' and 'inherently good' as
humanists in rose-tinted glasses like to think.

Here's food for thought: The same blood that flowed in Hitler, flows
in our veins...The DNA in Hitler and Stalin and Charles Manson is probably 99.999 percent similar to ours.

Today?...We've got tens of millions of kids around the world being DESENSITIZED to BLOODY GORY SCENES and BLOODY VIOLENCE
by video games and horror movies.
There is cause-and-effect there! That's a fact, and not an opinion.

You want to make a ruthless killer today?
For starters, desensitize him or her to bloody gore and violence.

Then, instruct him or her, on the internet, how to make bombs
[like those killers at Columbine did] or to exercise their reflexes
and responses in rapid-targeting and rapid-fire techniques by means of proactive video games [those with actual hand-held electronic targeting devices aimed at the screens; similar to that used by some military forces BTW].

Then obtain firearms either illegally, or stolen from parents,
or through some unscrupulous arm's dealers at gun shows.

Mix in a grievance, real or imagined, dispair or paranoia, and you
get tragedy.