Blood letting and blood drinking differ from the act of cutting oneself. The motivations might be the same, but the desired ends can be different. Blood drinking can be solitary, between two people or in a group -- whereas cutting oneself is almost always solitary. The main difference between the two is that the focus is more on the blood than the pain with blood drinking. Blood has historically been a powerful symbol in literature and art, signifying both life and death. Blood drinking and blood letting are always a case of taking the symbolic into the literal.
Vampiric imitation - Movies and other pop culture in the past years have done much to romanticize vampires. Vampires were once represented as demons and creatures of the devil in folklore. They were surrounded by superstitions concerning garlic, holy water and crosses. These days, partially due to contemporary authors such as Anne Rice, vampires have shed much of their superstitious air and come to embody the darker desires of humanity's ideal. The vampire has become a sensual creature of passion and beauty, immortally young, powerful, and free of inhibition. The vampire is no longer the murderous demon, but a symbol of what humanity wishes it could be: fearless, immortal, indulgent, powerful. I think that almost all young kids have a fascination or interest with the supernatural (aliens, monsters, fairies, witches and vampires). Some don't ever pursue it. Teenagers especially tend to find the vampiric symbol attractive when they reach a time in life when they feel very powerless, restricted, uncertain and anxious. This category consists of people who find pleasure in imitating the vampiric lifestyle. Some take it fairly seriously indeed. They do not kill to get blood, but they will drink from themselves or any willing donors using controlled cutting techniques (such as using a surgical or exacto knife or any other cutting tool that is precise, sharp and sterile). These people do not necessarily think they are vampires, but they enjoy playing the part. They are not usually the type to drink blood from a glass or drink an animal's blood. This category does not necessarily have anything to do with blood drinking as part of an erotic experience, although it can.
Curiosity and experimentation - Some people will try it just to see what it tastes like, how it feels, how the blood flows, what it looks like. These cuts will usually be made with razor blades or more crude knives (such as a pocket knife, kitchen knife or makeshift sharp tool). These cuts are usually fairly superficial and made in an easy to hide area such as the inner arm. This person will most likely end up doing it alone, but sometimes might be a part of a group that begins experimenting with blood letting and blood drinking.
Erotic experience - Sex is a way to share yourself with your partner. For some people, blood drinking can also be a part of this sharing experience. Often it is viewed as a more deeply bonding and erotic way to experience the essence of another person. It is the ultimate way to symbolically share your life with another. This would be an entirely consensual experience and perhaps a part of some fantasy role playing. This category always has to do with blood drinking as a sensual pleasure in an erotic exchange, although factors such as curiosity or vampiric fantasies may also play a part. As far as blood extraction, I have been told that if you suck on a particular part of the skin in a certain way for long enough, blood will come out. Sometimes blood is extracted by controlled cutting, or (depending on the inclination of those involved) with teeth or nails for those who into more "rough" sex or a "primal" experience.
Extremists: killers, religious cults, fanatics - There are some people that are extremists who practice blood letting and blood drinking for entirely different motivations than all of the aforementioned categories. These groups might kill a human or animal to get blood. They might drink it out of a glass. They may offer bloodshed as a religious offering and sacrifice. They may drink or let blood as part of a ceremonial ritual. These extremists often believe that blood is a powerful agent, that it can help one gain immortality. They use it to worship a deity. Blood letting or drinking may rarely also be a motivation for murder. There are a few people who sincerely believe they actually are vampires and are obsessed with vampires to the extent of becoming a fanatic. This person is not really religiously or homicidally motivated; they are delusional and probably disturbed. At the very least, they have lost the ability to distinguish fantasy from reality. These groups or individual extremists are very relatively small in number. Their fanaticism or criminal activity lands them in the media spotlight at times, but the destructive groups are not the whole of those who practice blood letting or blood drinking. An overwhelming majority of people who have engaged in an act of blood drinking will never come close to this category.
