So for me, the ‘hegemonic’ or ‘legitimating’ issues take a backseat to pedagogical ones properly speaking. That is, I know I can get butts in the seats and draw a paycheck for being a history professor in the current regime. And I know I can do that whether I actually get any history taught or not. But I’d like my life to be substantively meaningful, and to me substantive meaning always comes down to relations with humans rather than formal ideals of this or that sort. I’m pretty simple-minded that way.

But I don’t think that the lack of a justification for history is either a fatal problem or one peculiar to history alone. Similarly specious arguments about “critical thinking” are routinely produced in the context of a justification for studying English or philosophy. I have rarely seen anyone actually learn critical thinking in that way; either they substitute new received ideas (liberal pluralism, rah-rah Marxism) for old ones (down-home “good citizenship,” Christian fundamentalism) or they learn a bunch of canned responses to equally canned arguments. In English classes this often resolves to the mechanical application of “feminism” or “postcolonialism” to any given text, a mode which generally ceases to be productive as soon as the dramatis personae are identified, since the conflict is already pregiven in the interpretive framework. (Which is not to make any claim about the validity of feminist or postcolonial discourse in general, just about the way they’re often used).

This problem can actually be broken down into two parts, viz.:
1) The abstract problem of providing a foundation or a justification for this or that form of inquiry.
2) The concrete problem of justifying one’s own career for the purpose of obtaining or retaining employment/funding.

Now, at the moment 2 seems to be largely irrelevant, because as you very accurately point out, the petty-bourgeois populace at large is already fairly convinced that history (in the abstract) is valuable and should be encouraged as a part of the liberal arts. At the very least, the populace enjoys reading Stephen Ambrose and would like to promote the possibility of more Stephen Ambroses arising in the future. The fact that funds for humanities departments are being reduced in favor of hard-science departments is not something that can be solved by any particularly compelling argument–it’s part of a broader and more intractable systemic logic.

1, on the other hand, isn’t really a problem at all. If I’m a committed antifoundationalist and refuse to subscribe to the various activist interpretations of historical research, I don’t need to give any further abstract justification of my work than “I like doing it and I’m pretty good at it,” just as a poet is not always faced with the task of justifying poetry. The unhappy reality of life in a society where most work is make-work is that there’s no way to ground your own vocation. Sure, history is pragmatically pretty useless, but so is 95% of the bureaucracy and paper-shuffling that drives the American economy.

If problem 2 ever arises in a more acute way than it currently does, it will not be a problem of theory but rather one of pragmatics. The point is not to convince the people and the government with a theoretically bulletproof argument, but to bamboozle them with enough sufficiently compelling points that they continue giving you money. Pieties about “knowing your roots” and the old Santayana bullshit are pretty good at serving that purpose so far. Historians are a pretty smart bunch, so I’m sure we’ll be able to come up with more superficial high-sounding nonsense should the need ever arise.