There's something magical in the blood they seek that sustains them. I am not aware of all of the details, but I do know that killing is required to obtain it. More than that, death is considered an art form with them. It is not uncommon for them to arrange bodies on church steps as if in a play for their loved ones to find.
Anyhow, it doesn't much matter, as that is not here. I understand that consent is irrelevant in your world with regards to becoming a vampire?