Does Arendt not remind us that "morals" derive from mores, a word which, as the translation for ethos, bespeaks both habit and habitation? I ask: what could the polis be without habitation? While not asserting their isomorphism, can politics and habitation simply be divorced and one discarded like a useless marzipan dildo? Isn't the problem not the confusion of morality and the political as such but the oblivion of the originary sense of the polis itself?
I elaborate more where I am coming from on this question here, if you are interested in the topic.
It's true that Arendt treated mores and ethos as roughly synonymous, but I would argue that one of the crucial effects of the quarrel of the ancients and moderns is the fraught demarcation of these domains -- in my view, under the various modern assertions (and I include among these assertions romanticism, various avant-gardisms and pan-movements, post-modernism, post-post-modernism, alter-modernism, a-modernism, you name it, it's a big story) mores becomes "we-intentions" while ethos conjures, via public-ation, an imaginary audience including more than we-as-we-are-now, with certain extraordinary results (among them, finally, the modern Nation-State and, one hopes, soon a sustainable secular social democratic planetary polity).
Correct me if I'm wrong, but when you talk about oblivion to the originary sense of the polis, I wonder if you aren't mistaking Arendt's project in especially The Human Condition, as nostalgic when her point of departure there really was that the ancient world was gone for good. I agree that Arendt was enormously concerned with the loss of possibility that comes from a loss of awareness (which often follows from a loss of narrative remembrance) -- especially keen for her the loss of a sense of governance as civitas rather than as force, and the loss of a sense of politics not reducible to governance -- but still hers was not a project for the reclamation of the originary so much as an effort at rearticulation in the present from fragments at hand, among them pieces of the past make visible through argument, narrative, figuration.
My own understanding of a demarcation of mores and ethos is Arendtian in spirit (at least so it seems to me), and part of what makes it attractive to me is that it sheds light on some of the questions about the role of judgment that preoccupied Arendt's last theoretical works -- but you are right that this is a departure from Arendt, strictly speaking.
I would say assertions of modernity create its characteristic agon, especially one we might denominate "the cultural" (which seems to me defined by normative contestations between the work of morals and ethics in ways that would be unintelligible in their stakes to the ancients) and another "the social" (which seems to me defined by consensual contestations between the work of science and politics in ways and with stakes likewise unintelligible to the ancients).
Arendt has a lot of trouble with "the social" (consider its different treatment in On Revolution as against "Reflections on Little Rock," which has its share of problems, certainly), and my thinking about this -- which takes much from Arendt's "On Violence" as well as "The Conquest of Space and the Stature of Man" -- has helped me reconcile my take on Arendt with my feminism, and especially the centrality of Butler to my sense of gender politics.
You know, this is the sort of discussion that really sets me on fire, but which almost never finds its way to the blog, I must say. One ends up telescoping so much of what you are calling on in thinking through such questions that it ends up excluding too many folks who would otherwise read you, or else you end up producing a fully polished account you might as well publish in a more traditional way, since it ends up being more a settlement than an exploration anyway (and blogs, I think, are for exploring and connecting and contesting). Usually, these theoretical considerations appear instead as the iceberg tips in more conventional and polemical political formulations. Anyway, blah blah blah, thanks for the question.
By way of conclusion, let me add that I do not concede that a marzipan dildo would be useless. Off the top of my head I can think of any number of uses for one. Curses, I want my goddamn marzipan dildo!