When I saw that this was a Halloween-themed episode, I was a bit concerned. As entertained as I am by hot young women in costume (a given when Dean is involved), "Supernatural" is far more than fan service. Thankfully, the Halloween aspect was held to butchering of the meaning of Samhain (and the pronunciation, for that matter), and the rest was all connected directly to the season arc.
The witch Samhain was connected to one of the 66 seals holding back Lucifer, and this became the basis of a test for Dean Winchester. Apparently God believes that Dean is the right man to lead on the mounting apocalyptic battleground, and Castiel is apparently the one assigned to mold him into that form.
In this instance, Castiel is accompanied by Uriel, who seems to have a real chip on his shoulder when it comes to humans. Uriel doesn't seem to see the inherent value of humanity, perhaps due to the human tendency not to follow the rules, even when it's clearly a good idea. Uriel lacks the compassion that Castiel possesses, and this presents an interesting set of possibilities.
Is Castiel unusual for an angel, or is Uriel the one with the minority view? As powerful and close to God as they are, can it be assumed that the angels think and show allegiance monolithically? Nor can their nature be assumed as "traditional". After all, in the "Supernatural" world, demons are human souls that have been transformed and twisted by their tenure in hell. It certainly sounds like angels are something very different from humanity, just from this episode alone, but the relationship is not yet defined. Assumptions from various religious traditions may not apply.
Going to the source material (the Bible, naturally) may not give us a better perspective, since there have been clear deviations from the text in terms of the series, but it's a roadmap of sorts. Angels in the Old Testament were aloof and more than a little ruthless. Then again, God is also more smite-happy in that era, so it makes sense. For all we know, Uriel could have been one of those involved in Sodom and Gamorrah's "cleansing".
Angels in the New Testament, however, are generally more pleasant. That is, until one takes a peek at The Revelation of John of Patmos, in which case the angels are at war and they do not hold back at all. And for better or worse, that's the situation that is brewing; if Lucifer is released by Lilith, I imagine the end times come with the package. And it doesn't help that Sam is primed and ready to take the role of Antichrist Superstar in whatever gambit Azazel had in mind.
Perhaps, for the past couple thousands of years, angels like Castiel were more prominent. This particular war might have forced the deployment of more hard-line angels like Uriel. If angels are dying left and right to stop the opening of the seals, as Castiel noted to Dean earlier in the season, then Uriel's attitude could make sense. From his point of view, humanity has been given plenty of chances, and it may not make sense to Uriel for his kind to die to save those too weak to save themselves.
Could this be way Castiel is doubting right and wrong? Because that was the one point of the episode that didn't quite track. If Castiel was supposed to be more compassionate, perhaps he (and others in a similar function) are disillusioned by the sudden onset of war and death. Just as Dean balks at being asked to accept and even facilitate the deaths of thousands, perhaps Castiel questions the necessity as well. Because we don't know the full nature of angels on "Supernatural", it's hard to label it "blasphemy" when Castiel reveals doubt.
From the brothers' point of view, the notion of destroying an entire town and accepting the deaths of thousands in return seemed to be evidence that God was out of line. There are two sides to that argument. On the one hand, it was a test: not just in terms of what Dean would do on the battlefield, but how he would react to the