The idea behind Blood is that you are killing innocents to summon demons. So it would to be said you god has an evil streak, thus why not kill your own virgins?
Although LA Marigon is a bit funny, they are supposed to be about smiting evil yet I'm sure they get Blood access.... A case of the preacher standing at the pulpit preaching against sin and conjuring demons in their own time?
Read some guides about Blood hunting, don't worry about getting it perfect the first time, just go out there are find a few virgins, sacrifice them and open the gates of hell. Its quite fun.