Yet another post that started as a comment over at Chizumatic. Well, I’m having a bit of “I told you so” smugness about the ending, although I somewhat agree with Avatar’s argument. (Yes, even though I took the opposite position in the comments here.)
What I think can explain it is below the fold and behind spoiler tags, because they are fundamental to the series:
First, as he noted, QB’s entire race doesn’t understand character; that is, emotions. They think of them as a mental aberration when they think of them at all. So they’re not prepared to put in safeguards against things like wishing for time-travel, because the concept that anyone might repeat the same loop over and over countless times to save a friend is incomprehensible to them. To them, it’s an unknown unknown.
Second, we sort of assume that the mechanism of wish granting is Kyubey waving an ear and *poof* wish granted. We have no idea if that’s the case; they’re alien, and with advanced alien reality-altering technology that we can’t comprehend. Seriously, what sophont would intentionally create a goddess? What if it’s not Kyubey, but some incredibly advanced mechanism, an invisible (to us) “artificial genie?” All QB does is tell it “switch on, prepare for input from this human,” and then waits.
There is no review mechanism, because of the blind spot as noted above. It’s a bit of a stretch that in roughly 10,000 years, nobody made a wish to make them reconsider that idea, but I’m wiling to let the point slide; it is in character for the kind of people they’ve selected to not make such wishes. With Homura and Madoka, they had, for the first time, a pair of Puella Magi that had enough power, knowledge, and the will to do enormous damage to their system. It’s to Madoka’s credit that she only adjusted it slightly. Neither I, nor I suspect, Homura, would have been so considerate of the Kyubeans and the universe as a whole.
Two final points. I was left feeling a tiny bit let down by the 12th episode; it didn’t have the emotional wringer of the last 2, nor the tension. After sleeping on it, I realized why. The actually series climax is at one of two points. Arguably at the end of episode 11, as Homura begins to fall into despair, and then Madoka shows up. It’s obvious that she’s made her decision, she’s going to protect Homura and still save the world from herself, if she can. Also arguably, in the first few minutes of episode 12, when Madoka announces her wish; Kyubey realizes he’s been had, and she’s going to change the universe itself. I’ve gone back and forth, back and forth, and I can’t make up my mind. The purist in me says episode 12, the emotional side says 11 was the stronger moment. Essentially, 90% of episode 12 was denouement as we saw how the events played out in a slightly cosmic and abstract fashion. One of only two minor flaws in what is essentially an otherwise near-perfect showing.
The other flaw being a minor refrigerator moment in that Kyubey seemed only mildly curious that there was a puella magi running around that he had no memory of creating. And there’s two or three potential explanations for that.