There is no such thing as bad magick, only bad people who use magick to do bad things, Black Magick and Blood Magick amongst others mostly have a negative image as a result of the media and movies who have used "black" and "white" magick to represent good and evil, it's the same as the old cowboy movies where black hats and white hats were used to represent the good and the bad cowboy.
Just like the concept of yin and yang there is a balance in everything including magick, there is dark and light, day and night. The use of blood (ussually your own) in a spell infuses the spell with your presonal essence, finding spells that use someone elses blood or animal blood is rare, unless you're into traditional voodoo or something like that.
But it's allways important to remember, only do things that you yourself are comfortable with, if you feel uncomfortable doing blood or black magick, then don't but "white" magick can be used to do just as much harm as any "black", "blood" or "chaos" spell.