Huh… I vaguely remember reading a passage like that – the first five books are always harder for me to really get back into than the later ones, partially because I mostly do the Audiobooks and Marsters took a little while to pronounce everything right. I’ve gone through DM to a few passages that I thought might contain the goon-impaling, and I’ve come up short. Do you have the location in the book, or a quote?
If true – and I don’t doubt you at all that it is; I just want to read it in context – that does change a few things on my theory. It really makes things far more complex. The Knights defend freedom, free will, and choice. When confronting Cassius Snakeboy, despite knowing that he’s horribly murdered many innocent (ish) people, they cannot pass judgment on him and offer violence in order to stop the plague and save countless lives.
Michael’s expression was pained. “The Knights are here to protect freedom: to give those under the oppression of dark forces the chance to win free of them. I cannot sit in judgment of this man’s soul, Harry Dresden: not for you, not for anyone. All I can do is remain faithful to my calling; give him the chance to see hope for his future, to show him the love and compassion any human being should show another. The rest is out of my hands.”
In regards to Choice and Free Will, combining this with the actions of the angel in Ghost Story, I’m going to go out on a limb here and say that the Knights are free to defend those who are being oppressed by dark forces outside of their control, but are not free to defend people from the consequences of their choices. Put another way – if Nic sends five tongueless goons to attack Michael and he has no other choice, he
can fight and defend himself, because the goons
chose to do that. Michael wouldn’t make the little Denarian cult nervous in Skin Game if he had no power over them.
On the other hand, I don’t think Michael would be able to attack the Merlin on behalf of Molly. Molly surrendered herself to the will of the Council for judgment. If somehow things fell in such a way that Molly was still executed by the will of the Council, then it was in fact her choice to do so. She was certainly hoping for leniency, but chose to face the music rather than run.
But…… that wasn’t quite your question. You asked if Arthur decided to kill Molly anyways, against the will of the rest of the Council. Which would then not be an execution but a murder. And in that case, I am certain that Michael would be able to fight Langtry, and win handily.
And in fact, you also pose this as vengeance rather than defense of an innocent. This makes it trickier – the WG might not do anything for personal vengeance, but he certainly
does on occasion deliver judgment and wrath: see Murphy playing puppet to an angel herald in Changes.
OK. So, this is what I think, in all of the multifaceted ways it could be taken:
Michael attacks Langtry either to save Molly from execution or in vengeance after an execution, which was called for by a majority vote from the council: Michael fails; the sword breaks, and Langtry incapacitates him without killing him. Quickly and efficiently. He didn’t become the Merlin by collecting frequent flier miles, after all.
Michael attacks Langtry either to save Molly after Langtry decides to kill Molly despite losing the vote, or in vengeance after Langtry does it without the majority vote: Tricky. If everyone is stepping back and allowing Langtry to do it because he’s threatening them all and practically going warlock, then it’s a no-brainer. Michael overpowers Langtry's magic by force of will and through the sword. Because Langtry has little physical power and great magical power, if he either employs his magic to try to kill Molly or Michael, then the wardens and Ebenezer would join in to kill the warlock Merlin when it becomes clear that Michael gives them the upper hand. Everyone goes out for ice cream afterwards. But if Langtry is going ahead without opposition because the others either think it must be done or because the Merlin gets some sort of final say, then I think this reflects the will of all of the other mortals there and is also in a way the expression of the will of the council. Michael would fall in that case.
Michael attacks Langtry in vengeance not from Molly’s death, but from the deaths of all of the other children killed, like the Korean kid in the beginning of PG: I think that the WG would be behind this, and Michael
could prevail, but it wouldn’t be Michael vs. Langtry: it would be Michael vs. the entire White Council. And I think that attacking them in a room surrounded by wardens and several senior council members would be a deathwish. But then again, if that was the WG’s plan, I don’t believe that he would set up Michael in such a way. Michael
might prevail, but I think that it would be a Small Favors type of victory: he would probably accomplish his mission, but die in the process.