Yeah, I've seen Casshern Sins. That was a really great one. My favorite parts were the beginning episodes where it was basically just dying things trying to find beauty in a decaying world.
And honestly, yeah, I really enjoyed how fleshed out it was (the detailed descriptions of everything on the eye-catches is cool). And surely we couldn't have just 20 solid minutes of fighting every week, but I'd take more suspenseful/calculated fighting over listening to the main character any day.
Honestly, it's been like 4 weeks since I watched the 13 episodes so I'm having trouble recalling specifics, but the main characters motivation is basically just a glorification of vengeance, and the female sidekick is a celebration of psychopathy. That mantis example is probably the most over the top example I could cite though. But I just remember sitting through it and it seemed like a ton of dialogue was pushing really questionable morals.
I mean, I like the historical/human nature argument you're making here, but to rephrase it a bit, what you're saying could be applied to a study of the Nazis. "Hey, they took advantage of their circumstances and nearly got away with it. They were only human, can you blame them? Human's are backstabbing scumbags." But, I also like that you point out how intentionally gray it is. Perhaps I was misinterpreting it; I was just assuming that I was supposed to relate to or be inspired by the main character, but actually I'm supposed to see him/everyone else as disgusting (as I did). I guess in that light it's actually a really cool demonstration of the breaking down of right/wrong, good/bad. So yeah, totally Nietzsche.
But really, the more I think about it, I think it's totally legitimate to criticize the moral worldview or underlying social/personal messages of any anime. It's all really just TV shows and movies, which are comparable to books in terms of communicating or impressing morals. Likewise, it seems entirely normal for one to criticize anime for historical inaccuracies, dubious science, physically impossible phenomena ("that door can't open that way," "an arm can't bend like that"), internal inconsistencies, flat or underdeveloped characters, or just bad writing in general. So in that sense, with all of that being fair game for judging an anime, then I think questionable moral values is also something that's worth considering when discussing the quality of a show.
I mean, if Titan was all about preaching fundamentalist Christianity every episode, I'm sure people here (if they even continued watching it) would constantly lament that it continues pushing the gospel truth. People would likely criticize the series for devoting so much time to the lead character talking about his heavenly reward and trying to convert all his friends. Imagine if such moral values were being pushed through in between bits of what you really care about watching (the sky-surfing grappling hook giant slashing).