Foreigner
Bluelighter
There are a lot of Voodoo practices that involve slaughtering animals and drinking blood, etc.
Not to mention placing (violent and non-violent) curses on people.
If that isn't dark, I don't know what the fuck is!
Just wanted to interject here. First you say Voodoo isn't real, then you make claims about what happens in Voodoo.
Voodoo (African), Hoodoo (New Ordeals) and Vodou (Haitian) are real by virtue of them being real spiritual practices. Use Google to find out more. They're real. Voodoo is the established religion of many African countries.
As for curses and what not, yes it's true. They do a lot of curse work. They also do a lot of healings and "white" magic too. You can't just write off a system as a whole because there are aspects of it that bother you. Every major world religion has dark mysticism in it, and workings that can be used to harm others - including the Judeochristian faiths.
The animal sacrifices are part of the deity worship and have specific purposes which are very important within the context of the faith. Within that context, it is not considered dark, but spiritually invigorating. Sacrifices in of themselves are not dark. In most cultures that sacrifice animals or even humans, the living thing being sacrificed is considered a position of high honour because of its transformational nature. Again, some research will uncover this. I don't see how that's anymore dark than the way we treat animals in our corporate farms. Sacrificial animals are treated like gold until the day they die, unlike our livestock which get clubbed or electrocuted before processing for their choice cuts.