And which one of those are undeniably good example? Judging by Demands of the Qun that magister would have achieved better results with fireballs. The rest are questionable at best and atrocious at worst.
Not the best example given that this was written by someone opposed to blood magic, but consider this:
(1) The criticism of Tirena of the Rock is not based on ethics, but on pragmatism. That her spell was less efficient than another she might have used says nothing about the morality of the action, and since she didn't damage anyone but herself and the acceptable targets I can't see any ground for condemnation. Also, the criticisim is based on the qunari's reaction, so it would've been perfectly fine to use the same against another acceptable target.
(2) The lovers' example is completely false. Blood magic in general does not require a death, and anyway if the caster only uses their own blood there's no ground for condemnation. Anyone can choose to die.
This Codex entry is an example of the nonsensical reasoning some people in-world use to justify the idea that blood magic is evil. That is unsurprising, since if people really want to believe something, they will use nonsensical "reasoning" if necessary. There are millions of cases where belief overrides any other mental faculty.
The really frightening possibility is that the writer who wrote this didn't just put beliefs into fictional people, but might actually believe their own "reasoning". I have a hard time believing that one of the experienced writers would make a magister use such obviously flawed logic, so it's quite possible they gave the task to someone who never engaged in moral reasoning before.