They're coked up, probably. You can do anything if you are on that shit (or something like it), especially if you are a sociopath (or something like it). Even Roy DeMeo was reportedly drunk or hungover almost constantly.
Yeah I imagine they have to be coked up when they first start but they probably get desensitized after a couple of times doing it. I've read that the Familia Michocana members were told to dismember petty thiefs or rivals to get used to the seeing blood and doing crazy shit. I think if was La Tatuta the current leader of the of the Knights Templar that told his new recruits to do that so they can desentized.
