I think killing comes down simply to "power and control".
The vast majority of killings (or murder) are because someone either wanted power over someone else..or wanted to control a situation (or both).
And yes of course there are "boredom killings by the ethically or morally bankrupt (depending on their societal guidelines) ...but on closer inspection, many of those can be attributed to the P and C thing too.
As long as people are able to distance themselves so that they can perpetuate a self-lie , they seem quite happy with killing their fellow humans. If they can go to bed without undesirable images rearing their ugly heads, and their brain saddling them with guilt , they can easily dispatch bomber planes, snipers, tactical units or push explosive remotes til the cows come home and think little of it.
The ones who are using the long distance techniques, IMO , are not the ones to be wary of ....it is the ones who can happily use a pencil or a pen, or maybe even a knitting needle to do the job ... the ones who can easily look you in the ey as they slide a blade in. Those are the ones to avoid.
Humans have a propensity for violence that knows no bounds, and all it takes to enable it is the right stimuli ( ie paedophilia, rape ..or some such emotive crime). Break down their tabbos and give them a reason that they can quell their guilt with , and even granny would peel you like a ripe tomato with her dainty little paring knife.
As a couple of people have commented ..perception ...what you percieve is how you will respond.
Now...that nosey neighbour has been bothering me all afternoon with his flatulant comments to me over the fence ....where'd I leave that trenching shovel ???