Spoiler Alert, big time. Spoilers for a number of Stirling works, including "Emberverse" and the Draka-series.
In terms of Christianity and its portrayal: I'm Jewish, and Brother Ignatious almost made me want to become Catholic. First of all, he's awesome, the complete and absolute ideal of who you would want as a spiritual advisor, friend, and co-combatant. Second, the way he draws on his faith to support his character, and his character is extremely appealing. (In general, he's very positive, non-judgmental, very warm, never whines or shirks or anything stupid.) AND he has a meeting with Saint Mary, which is portrayed as at least as "real" as any of the Wiccan encounters depicted with MacKenzies and Mackenzies. And, oh, by the way, the Pope is a background figure of heroic dimension, and the Anglican and Catholic churches have re-united. To top it off, the frisson accompanying Brother Ignatius's battle-cry almost makes me want to be one of the Pope's Marines or something like that.
Re: Dogging the past: I think something interesting that Stirling does is get sufficiently into a character's perspective that he ends up being accused of endorsing that character's perspective. Remember, when he was accused of being pro-whatever-the-Draka-stood-for including his not-so-happy ending for The Alliance For Democracy, he replied, "It's a dystopia, you twit."
Keep in mind that for every part showing Walker or Vashon having the time of their lives, there were parts showing Alston and Cofflin grimly doing the hard work of saving the world from Walker and showing Kustaa or the LaFarges having to suppress strong revulsion when in Draka territory.
There are parts showing Havel and Juniper at times genuinely ruing the loss of pre-change benefits. (I think it was Juniper or Denny who very quickly grasped that the end of fire-arms would actually be a Very Bad Thing.) Havel, conducting the annual change-day ceremony, has that private sliver of hope that the match dropped on the gunpowder will spark a different reaction.
I think that a lot of what you see with the post-change cast expressing about their world reflects growing up with adults who reminisced about pre-change things. If I can figure that out, then I imagine Stirling meant for that as part of a character's perspective, and, not his endorsing the idea of bringing the world to such straits.
If you want something comparable, look at World War Z. A couple of interviewees talk about the good things that have come from the disaster that they struggled with, such as people getting re-acquainted with honest work, strong communities, etc., but no one with a stitch of sense is going to say, wow, they're really glad the zombie epidemic happened.
I think that WW3 book from the early 1980s --the one with two guys trekking across the country to See What's Happening in America after the big kabooms-- there's an accentuated appreciation in interpersonal relationships --the two friends embrace instead of shaking hands-- and affection for a Dodge Dart not affected by the pulse-thing. (EMP, I think.)
I think in a lot of post-apoc/dystopian narratives, you will see at some point a perspective of appreciation for whatever thin silver lining can be had from the mushroom cloud or otherwise.
