Hoisted from Comments: Cosma Shalizi:
The practice of one member of the discipline isn't enough. If it was, I could point to Sam Bowles and Herb Gintis and say that being an economist means a profound engagement with traditions of social thought broadly inspired by Marx and emphasizing the contingency of social roles and institutions, but corrected by evolutionary game theory. Or I could point to Mark Blaug to say that being an economist means according basically no normative weight to the two fundamental theorems of welfare economics whatsoever. Or I could point to Edward Prescott and say that being an economist means re-inventing statistical wheels, and deciding that they should be hexagons. Or I could point to D. McCloskey and whatever it is they're into this decade.
I don't think "Berkeley economist" will do. There was a reason I specifically mentioned Varian's micro textbook, and Varian and Shapiro's business book about profiting by exploiting customers and manipulating standards-setting.
I think that, as the discipline has developed, the thought of The Theory of the Moral Sentiments and even much (most?) of The Wealth of Nations has, in fact, become profoundly alien to what most of the profession sees as the core ideas of economics. This could change; I hope it does change; if it changes, I expect that the practitioners' histories will edit out the fact that it was a change.
If I had to put it in a slogan, I would say that it's not so much that you're not an economist, as that you (like Sam and Herb) are a harbinger of a different and better economics.
I think my response has to follow three tracks: what your standard economist does, what I do, and what the canonical political scientist does.
First, your standard economist is not "Hobbesian"--does not enter a butcher's shop only armed cap-a-pie and only with guards, fearing, as a Hobbesian would, that the butcher will not sell him meat for money but rather knock him unconscious, take his money, slaughter him, smoke him, and sell him as long pig. A Hobbesian does not buy and sell goods and services in mutually-beneficial Pareto-improving exchange relationships. A Hobbesian finds the biggest bad-ass in the neighborhood, and swears liege homage to that bad-ass in return for that bad-ass's promising not to kill him. Your standard economist is, rather, a "Lockeian"--presumes that there is an underlying order of property and ownership that is largely self-enforcing, that requires only a "night watchman" to keep it stable and secure.
Now it is true that your standard economist is a largely-unreflective Lockeian: does not inquire why one trades rather than takes, affects the tough-guy pose that it is only the repeated-game nature of economic interactions that keep us from always winding up in the bad cell of the prisoner's dilemma, and adopts the reductio that humans are narrowly self-interested only in material acquisition (in order to strengthen the case that the social apparatus of voluntary market exchange produces good outcomes--to make the point that even private vices produce public benefits if they are constrained by the market). But that the standard economist is a largely-unreflective Lockeian does not mean that they are a Hobbesian.
When it comes to what the standard economist thinks, I think that the example of Hal Varian cuts the other way than Cosma thinks it does--or at least cuts ambiguously. Varian's graduate micro textbook is the formalism: people don't just take stuff because taking stuff is not in the strategy space. Varian's lectures and seminars are considerably more nuanced. Varian and Shapiro's Information Rules is intended for a business-school audience, and the object is to create barriers to entry so that your firm can profit. When he teaches not in the business school but in the economics department, Hal says, he still assigns Information Rules in his antitrust, regulation, and industrial organization courses, but--in the immortal words of Frederick von Frankenstein, he "changes plus to minus, and minus to plus": not the creation but the destruction of barriers to entry (as long as appropriate incentives are left for innovation) is the object.
Second, I do agree that I do--and other economic historians do, and Bowles and Gintis do, and McCloskey and Blaug do, and a bunch of the rest of us do--something somewhat different than what your standard economist does. But I view what I do as making the preconscious or the unconscious in "standard economics" conscious. And I would appeal not to the formal theory of the graduate textbooks, but to the actual practice of the economists I know as the test of what "standard economics" is.
It is true that back in my senior year of college it seemed to me that I was too shy to be anything other than a professor and should become one. I looked around, and discovered that the people applying for jobs as assistant professors of history and social studies were 40-year-olds who had written two books while the people applying for jobs as assistant professors of economics and social studies were 26-year-olds who had one half-written article. So it seemed a no-brainer to me to go for a Ph.D. in economics. But the fact that I made that decision demonstrates that I am a real economist after all: I regarded (and regard) responsiveness to market forces as a moral virtue, while if I were really a historian in disguise I would regard responsiveness to market forces as a moral vice.
Third, it seems to me that your standard political scientist's conception of the standard economist as "Hobbesian" is an exercise not in interpretive understanding but rather in disciplinary line-drawing--and, perhaps, attempted disciplinary imperialism: if the core of economics can be defined to be as small as possible, that leaves more space for political scientists to play.
Remember: there are real Hobbesians about. They are the international-relations realists in political science departments--not the economists in economics departments.