One thing I find really interesting about this story is that nobody has any idea what's going on, and nothing is going according to anyone's plan.

(1) It seems clear that Hat and Cloak = Quirrellmort. Less clear, but still likely in my view, was is that the point of this plot was to eliminate those friends of Harry's who would make him resistant to manipulation by Quirrellmort ("Lessson I learned is not to try plotss that would make girl-child friend think I am evil or boy-child friend think I am sstupid," Ch. 66). Instead, while the plot may be the end of Harry's friendship with Draco, it's probably strengthened his bond with the morally pure Hermione, and convinced some members of the Wizengamot that Harry is Voldemort, which probably doesn't have a place in Quirrellmort's plans. Furthermore, Quirrellmort may not realize what he's done.

(2) It occurred to me that giving Draco Veritaserum might have made Lucius realize that Harry is not Voldemort. However, if you look at some of Lucius' dialog closely, the subtext appears to be, "Dark Lord, you have lost your humanity, and therefore cannot possibly understand the love I have for my son. I am willing to risk your wrath over this, especially since I suspect you are much weaker trapped in the body of a child. And why do you bother telling such ridiculous lies about your motives?" If Lucius knows that Harry confessed to Draco that he had no idea what the conversation in Ch. 38 was about, Lucius probably dismisses that confession as a well-told lie.

(3) Dumbledore believes that Harry has just signaled to Lucius and the other Death Eaters that he will pay any price to save his friends. But Dumbledore is wrong, at least about Lucius. Lucius believes he has just fallen victim to an incomprehensible plot of Harrymort's, possibly designed solely to torment Lucius, and therefore does not see this as relevant evidence to how far Harry(mort) will go to save his friends in the future. Indeed, Lucius accused Harry of lying when Harry explained that "his stake" in the situation was just that Hermione was Harry's friend.

(4) Harry is deeply conflicted about his actions. Yet there's a case to be made that that Harry's decision making process (the one he's now feeling conflicted about) was better than Dumbledore's. Not perfect, but better than Dumbledore's. Not only is Harry ignorant about the consequences of his actions (as described in points 1-3 above), he was in the no position to know anything at all about those consequences... except for the consequence of "save a little girl from getting eaten by Dementors." Under those circumstances, Harry's arguments in Ch. 77 may actually apply here. Unfortunately, that may mean Harry ends up learning the wrong lesson from this incident.