Alrighty, I'll ask the question: what are your views on blood magic in general? Useful, abused, beneficial, misused, good, bad? This extends to anything related to blood magic as well, from the Joining to Reavers to the few rituals we see in the series. Also, did you use it for yourself or your companions in any of your playthroughs, and how did that go, if so?
I think that, like all things in between guns, swords, and tactical nuclear devices, it all really depends on the eye of the beholder.
Now I'll start with my opinion/belief that blood magic is merely a tool; that's it. The Chantry casts a deep pall over it, and perhaps a portion of the problem is that the Southern Mages believe just that; it's inherently evil. Also without anyone learning, teaching, or actively practicing blood magic, demons have an easy in for possession (though I can't see why a demon, who has no blood in the Fade, would know anything about blood magic, as they don't need magic themselves in a realm where thoughts and wishes can come into existence).
I don't really recall any incidences of any Tevinter mages turning into Abominations. You would think the White Chantry would be crying left and right about that, but all they mention is blood magic and SUMMONING demons, not turning into them.
And that brings me to my next point; Tevinter knowledge and experience with blood magic. I know that it isn't public/open, but then we're all winking and touching our noses at that idea. Denarius (in DA II Act I when Fenris decides to go Punisher on him) summons a whole fleet of demons (shades, arcane horror, abominations... usual Vint Arsenal) but doesn't get turned himself. The Venatori mage that was slashing Warden throats didn't seem to have any real issues, knowing exactly HOW to turn a Warden into a demon and enslave a Warden Mage (yes, Corphy taught him... knowledge and experience). So I think that blood magic is 'useful' in the right hands, and perhaps not necessarily evil unless the intent (or act) is evil in of itself.
Having said that, I can think of at least three great uses for blood magic.
Healing - Seriously, if the guy just took a sword to the gut and is spilling red stuff all over the place, I don't see how this would be 'evil'. You're not taking blood, using it for power, trying to control someone, or turning them into a steaming slag of gore and bones. Healing him with his own blood (and stuffing it back inside) sound pretty beneficial considering blood magic is more powerful than regular magic and Lyrium-fueled magic.
Periods - Uh oh, I went there. But lady mages certainly have that advantage, don't they? But again, blood that isn't taken or start cutting one's wrists. Certainly redefines 'that time of month'.
The Harrowing - Obviously this is a Chantry solution into creating the boogeyman. They're stuffing demons into poor kids heads just so they can wave a flag and be 'technically' correct about the threat a mage imposes. But you didn't see Bethany have any issues being a free-born mage. Likewise, Solas didn't seem too worried either. Jowan was a full-blown unHarrowed Southern blood mage stuck in a haunted castle with demons and the walking dead... and remained human in an obvious Veil-Tear (but couldn't open the cage he was stuck in despite being a mage). Merrill was practically the Son of Sam without changing, and the Dalish Keeper from Origins (Varathorn?) practically shared a spirit/demon to live for centuries (with the elves blissfully stupid at this rather odd point while singing Duran Duran's "Hungry Like A Wolf").
So to me blood magic is like regular magic is like a sword; what are you doing with it? Yep, slitting the throat of a dozen slaves to make your tea is a bad thing. Cutting your own arm to defend yourself from someone trying to kill you? No, probably not a bad thing (get tetanus shots, first). Using it to heal someone? Good thing, IMHO.
And I don't actually believe the lie about the susceptibility of the Veil and blood magic considering the Magister Sidereal had to glut something like a hundred thousand slaves along with Dumat's Canticle To Overthrow Heaven to send seven people physically in the Fade. Millennia of blood magic didn't have a Breach opening up over Minrantheros, so I think Thedas might be okay.
I wonder of Qunari Sarabaas practice blood magic. All that hate on magic but they're not afraid to weaponize their own people (in a way that makes the Gallows look like a petting zoo).
What do you think?