There's a half-joking analogy about the difference between involvement and commitment relating to breakfast. When you look at a plate of bacon and eggs, the chicken was involved and the pig was committed. This also applies to the question of sacrifice. I see the question of "should we do some kind of blood sacrifice" come up sometimes. The knee-jerk reply that comes back when it arises is, "Donate blood and dedicate the act." Dedication is not sacrifice the way eggs are not bacon.
In the ritual deposit areas in Celtic tribal lands, researchers have found weapons that were deliberately broken before being cast into the pits. From what they can see, the weapons were being given over to the gods. I don't know if there's anything in the Celtic lore about a weapon being dedicated to a god, but when someone does that in other traditions' source material, they get to keep the weapon and it is used in this world. If you donate blood and dedicate that act to the gods, the blood stays in this world and is used here. That is why it's a dedication. If it were a sacrifice, to follow the form established in the past, you'd need to pour the same pint onto a fire, thereby transferring it to the Otherworld for the gods' usage. Also, there is a distinct difference between bleeding yourself to the gods and using a different animal's blood. Using your own blood can be taken as a sign of an even deeper commitment to the act than may be intended. I'd much sooner see people buy some pig blood from a butcher or use ghee as the Hindus do to ensure the wrong message isn't transmitted. Of course, if all the signs say, "Do it yourself," who am I to question if they do it safely and sanely?
This is not saying people should go to a blood bank and try to talk them out of keeping the bag of blood you generate for them to do a "proper" blood sacrifice. What I'm saying is that if you're going to sacrifice something, some part, if not all of it, is supposed to go to the gods. In short, it has to be ritual bacon. So it is that people dedicate themselves to gods instead of sacrificing themselves to them. The latter implies ritual suicide.