The Army would have you believe that killing is a very unnatural thing for most people to do. The expert shooters in bct were warned that when they actually found humans in their crosshairs that all of a sudden they may be incapable of shooting because their body would subconsciously rebel against the act of killing another person and throw their shots off. Basically all the time you spend doing marksmanship training is to override the dormant subconscious belief in humans that killing other humans is unnatural.
The people that killing comes naturally to, I'd say they have something broken in their subconscious somewhere or they get that training from their own sort of self inflicted brainwashing.
It's a complicated issue with many different factors.
If WWII Russia is to be believed one of their top snipers was female and I believe her final kill tally was upwards of 500. Could be propaganda, but even if you gave her 1/4 of the kills that still totals upwards of any of the other countries top snipers in the war.
I believe that most anybody is capable of horrific feats. But won't deny that males generally seem more involved in the mass killings.
Edit: Russian sniper lady had 309 kills.
