Or the natural world doesn't care about our opinion of good and evil and just abides by its own rules. How much death and destruction has Mother Earth inflicted on its population? That doesn't make her evil. How many soldiers have gone into battle to create pain, destruction and more war? That doesn't make them evil, just soldiers following orders. My metric for evil is pretty clearly different from most. But my metric means that you can't justify actions on a good/evil basis. You have to take every action and consider it as it relates to yourself. i.e. which side of the gun are you. Just know that at some point, you might be on the other side of that gun. The Shedim are evil because they are pointing a gun at us. When we point that same gun at let's say a tasty pig, then we are the good guys.
The big issue I have with blood magic is actually the same with using reagents (some of which are parts of sapient creatures by the way). We in the sixth world are using what the 4th world called Raw Magic. Raw magic is tempered in the 6th world by drain. We don't use too much power because it hurts. Blood magic, and reagents, lets someone else pay the price (either in pain or in labor). What that does is dump a whole lot of energy into the manasphere, which in turn attracts astral denizens. The Great Ghost Dance wasn't bad or evil because it was blood magic, it was bad because it was so powerful. Of COURSE dragons don't want us lesser species using it, that would put us on par with them.
A similar thing happens with toxics. Hey, look, we figured out a way to manipulate astral space so that we can use it and dragons can't. Dragons didn't like it in the 4th world, but it was difficult back then (see Ritual of the Thorns). Now, we can create special magic zones over night.
Both of those examples involve mundanes helping to boost the strength of magicians. Humanity has figured out ways of fighting magical creatures by using their numerical mundane superiority... and the dragons are pissed. So of course THEY think it is evil, the gun is pointed at their heads. And who is coming out and calling Toxics and Blood mages evil, to the point of putting illegal bounties on their heads? That's right, dragons. Did you notice that same dragon didn't put a bounty on insect shamans... even though the Chicago incident happened like a year earlier? Why is it that humanity boosted magic techniques are evil, but alien, other worldly boosted traditions are given a pass?