Blood sacrifice has been around before you and i and will be around after. the SRI MAD DEVI BHAGAVATAM Book 1 ch 18 vrs 57-61 states that "the killing of animals in a sacrificial ceremony is not a killing; it is known as ahimsa(non-killing); for that himsa(killing) is not from any selfish attachment:therefore when there is no such sacrifice and the animals are killed out of selfish attachment, then that is real himsa: there is no opinion on this. smoke arises from the fire when fuels are placed in it;and smoke is not seen when no fuel is added. So the HIMSA, as prescribed in the vedas, is free from all blemishes, selfish attachment,etc and therefore it is unblameable. So it follows the Himsa comitted by persons attached to objects, is the real himsa; that can be blamed, BUT the himsa of persons who have NO DESIRES is not that sort of himsa. therefore the learned men that know the Vedas declare that the himsa done by the dispassionate persons, with their hearts free from egoism, is not himsa done at all. O' Dvija! really speaking the killing of animals done by the house holder attached to senses and their objects and done under their impulses can be taken into account as a real act of killing; BUT of those whose hearts are not attached to anything, of those self controlled persons desirious of moksa, if the do an act of himsa out of sense of duty, with no desires of fruits and their hearts free from egoism, that can never be reconed as a real act of killing.(57-61)