Dark Magick is not the practice of using Magick to harm others, its very much equal to Light Magick. Dark Magick is more freely used because of how it mostly does not harm if used correctly
I practice Sorcery which is seen a Dark Magick, but I have never harm anyone. When I give blood to my Goddess, I use my own Blood or one of someone who consents to it.
This is not breaking the wiccan rede because I am harming no one, and Blood is a great offering to the Goddess
The Dark Sorceress,