Fucked in the head, I except. Some sorta severe serotonin deficiency perhaps. Looks out into bright happy smiling hot sunny days in the world and sees desolation and a race bent on self destruction and the fucking up of the poor majority by the obscenly rich majority. Messed up loser scumfuck who oughta be exterminated. Get some kinda sick pleasure from trying to engender visceral reactions of disgust and revulsion in their audience, maybe even enjoy the flames. Exposed to horror stories at a young age and had 'em imprinted on the psyche. Watership Down's rabbits had it tough. No desire to hurt anybody else, but find writing helps feel better sometimes, whether gory splatterbang or just warm and fuzzy.
That's just me, of course. Only me. You with the pen and the hatchet quit getting all offended. I'm sure the others who've dabbled in dismemberment fiction are all lovely well balanced people you'd be quite happy to take home to Mother. Stephen King, I think it was, did a very good essay on the nature of writing and reading horror and such. Undoubtedly there's a few other things on it as well.