I really don't have issue with such games existing, or the people who play them- but I personally don't see the appeal.
I know some folks worry that only people who are considering such actions in real life are interested, and that's a downright falsehood. Some of the nicest, most gentle people I know consume the most vile-appearing media I've ever heard of (example: I have seen A Serbian Film turn up on Christmas wishlists before.) I have no idea why they're interested in this stuff, but I've only ever seen them watch it- not a one has even come close to attempting anything from these sources. I've been tempted from time to time to ask why, but I don't want to come across as disapproving- after all, these are great people who help friends, give to charity, worry about hurt wildlife, and just happen to occasionally watch gross movies (and never expect anyone else to). It's not a bad thing, it's just an odd thing to me.
The worst experience I've had playing a game was when I got one of these friends a used copy of Manhunt for the Wii as a gift. I wanted to make sure it worked, since it was used, so I played a bit of it. The beginning calibrates/teaches you the motion controls over a black background... you are instructed to mime out a stabbing motion, at which point blood splatter pops up on screen, along with screaming. I have never wanted to turn a game off more in my LIFE!