This is an awesome thread, it is not to be taken lightly indeed. do not give blood to any deity, spirit or anything in between if you cannot fully trust them! I have learned quite a bit I did not know in the past, thanks for posting!
But didn't the Aztecs, etc., give the blood, not of themselves, but of unwilling people who they went around capturing for this purpose? They did not sacrifice of themselves, but that of others. How can this be honorable to gods? I think Brysing is right to point out those who "cut" needing help, as he was talking of those who cut to rid themselves of pain they cannot deal with, a depression of a sort, a release. He was not talking of giving to gods. But this could be misunderstood by the young ones as reason to continue the hurting of themselves, when what they really need is professional help.
Incorrect , the aztecs primarily sacrificed their own. Sacrifices of prisoners of war were a minority in comparison , and held no high devotional value. Nor did they capture random people , hollywood makes such things up. The aztec and mayan need for shedding blood for their deities was born from the harsh environments and conditions they lived in. It was seen as either the only way to sway a wrathful deity or to give another deity enought strenght to balance the fragile equilibrium of their world. Prime example of a highly devotional sacrifice would be Toxcatl (which is the only ceremony in which the heart of the sacrifice is cut out with an obsidian blade) which occured once a year , and a volunteer or "perfect male specimen" would be chosen and treated as a god (in particular the god Tezcatlipoca) for an entire year , given anything he desired and treated as he wished , at the end of the cycle on the Toxcatl he would be sacrificed to the God he was representing (Tezcatlipoca).
The sacrifice of prisoners of war was mainly as a fear tactic or an actual devoting of blood itself to their deities. Teyollia the essence found in Eztli (Blood) was seen as the epitomy of that which is physical , and the essence used to exert change in the physical world. Hence large amounts of blood were often sacrificed to a deity who needed the strenght to "defeat" the deity that currently resided as dominant in the equilibrium. People who cut themselves for emotional pain need help , people who use blood in their practices do not.
I know in this society the human sacrifice practiced by the aztecs can seem shocking, technically it is murder. However, the people to be sacrificed must have been willing.
Perhaps that is hard for us to understand, but I would imagine being chosen to e sacrificed was a great honour and there would be spiritual rewards promised in the afterlife- which they would thouroughly believe in.
Personally I go by Crowley's advice in Liber ABA-
"But the bloody sacrifice, though more dangerous, is more efficacious; and for nearly all purposes human sacrifice is the best. The truly great Magician will be able to use his own blood, or possibly that of a disciple, and that without sacrificing the physical life irrevocably."
Of course, Crowley's 'blood' was not always blood, but a symbol for another possible substance one can use.
Personally, I have only used actual blood very little in my workings, I believe it gives me more of a psychological shock rather than raise anything powerful; then again perhaps I am not using enough!
I think sacrificing a horse would be far too messy and would attract the attention of neighbours!
I know the old pagans/phonecians around 2000 BC were practicing this. Its an old outdated practice but it works and it can be the most amazing experiece or extremely frighening both of which I enjoyed but when things started to actually happen I had to stop. However, like with most habits and rituals they become hard to stop so I did relapse once this year.