Harming something/one is a perspective thing. Everytime you breathe, you are killing millions of microbes. Do we quit living to appease bacteria? Everytime we walk we are killing thousands of invertebrate creatures, yet do we quit walking to save these creatures?
Everything we do ends up harming someone or something. If a sacrifice is done for the right reasons, and the sacrificee willingly and knowingly gives him/herself over for that purpose, I say that the Rede isn't necessarily broken...
Any other thoughts? I don't practice any sort of sacrifice, but I think this post brings up an interesting rhetorical question...