All bloodshed weakens the Veil. As does all magic use.
I've read and re-read WOT and saw no mention of a definitive corruptive force in blood magic. This isn't Star Wars.
Fine I will quote Gaider for like the millionth time on this forum:
"Blood magic isn't inherently evil, but the temptation to do evil when you have the power to bend others to your will must be insidious." -David Gaider
"It's not corruption in the way that the Blight is a corruption... A lot of it is opinion and fear, [of] the things that a Blood Mage is capable of. Which, as we're moving forward, we'd like to show that a little bit more, especially the mind control. And it is based on people who have that kind of power, the ability to influence other people's minds, the temptation to misuse it is a corruption. That kind of power is corrupting, right? That's the danger, not a physical 'I suddenly turn to the dark side and my eyes have gone black' kind of corruption." David Gaider
Also
Cameron Lee:
Cameron: Blood magic is an interesting one. Pure blood magic in the lore of the game is really supposed to be a very evil power. In previous games it wasn't really perceived to be that way. We talked about it being that way in the lore, we'd talk about crazy mages who went down the blood magic route and how that would have nasty consequences. So in Inquisition if we can't bring that across, that consequence across then we won't do it. We're looking at a couple of different options that still give that quasi-evil kind of fantasy element without trying to go into the nitty gritty of blood magic conflicting with other elements, but we haven't landed on which one's going to be there.
I never said it was the Dark side of the force. However, it is the corruption of power in human nature that makes it corruptive. If you have the ability to make other people do what you want them to do, it is an extremely temptive and corruptive temptation. As Gaider says, you may start off doing it for their own interest and don't notice you are crossing a line.
Also, just read Last Flight.