Well this is certainly a creepy demon but that's no shocker if you watch Charmed since Dr Hack N Slash was also Barbus who was creepy on that in both forms and in this one he was even creepier looking. This dude found a way to keep on living long past his expiration date which required taking parts from people. So he'd jump the unsuspecting person in a parking lot like that poor guy who ended up at the hospital literally holding his guts in which was pretty gross.
Since Sam is just so very desperate to save Dean he doesn't think and decides that maybe this guy is the answer to their pressing problem since Hell is nipping on Dean's heels. I don't want my boys looking like that creature. Sure he might have been human at one point but that was long ago since he's a monster now and not looking too pretty. Could you imagine the Winchesters going around looking like that? I couldn't and not want to since that's just wrong.
I do wonder why they didn't bury the guy better since someone just might stumble across this guy and let him out. They should have burned the book along with the guy. Well can you burn a guy that technically can't die? Who knows since I have no way to test that theory. I'm unaware of any freaky people around that steal peoples organs to keep on living. It seems that John was only able to get this dude's heart but he kept on ticking with a new one. Now he's stuck in the ground until someone finds him. The guy isn't dead which means someone could hear him screaming for help so that was a bit sloppy boys.