Okay, I am saying "weak" in the sense that they were not strong enough to not pull off what they wanted without resorting to something that is drawn from suffering. If the mage was "stronger," they wouldn't need to do that and still pull of what they wanted. Resorting to blood magic means the mage should strive to get better so to not have to resort to such wickedness.
Blood Magic is a crutch. It is a boost to magical power, but it is a power that is drawn from immoral means (drawn from suffering/pain/harm).
I do see reasons why people should limit themselves if it is to prevent evil/wrong from needlessly being done.
If one has to resort to blood magic to save a bunch of children, okay, I won't really fault them for it. However, they resorted to something that is dangerous and is rooted in suffering. It would be better if they didn't have to, if they trained themselves more to not need to resort to something like that.
Solas has had many centuries of growing in power, and for a while he was weakened, but he does show (with his basilisk ability and such) that blood magic isn't necessary to perform strong magic. One can try to use enchanted devices and such to augment magic, instead of resorting to blood magic.
A mage using lyrium or not using blood magic can still be a villain (and go against the will of the Maker, and I say this because if the Maker is real, then what the Maker dictates is the truth of the reality he created), but that doesn't make blood magic any more innocent. Fade magic is not rooted in harm, blood magic is. You cannot have blood magic without harm, even if that harm is no more painful than a hair being pulled. Fade magic does not grow in strength from pain or death, but blood magic does because it is tied to "life force."
I don't think it is a problem knowing blood magic, but it should be a discouraged thing and a last resort. In my opinion, anyway, constantly going with the end justifies the means will corrupt an individual.