The really pure public choice view is that in the market and in politics, the same human motives are operating. They just operate under different institutional rules in each case. The less doctrinaire view would say that social norms also may differ between the market realm and the political realm. In theory, it is possible for the norms of political behavior to attenuate the tendency toward inefficient and predatory outcomes. How well this works in practice is certainly debatable.
Yes. Exactly so. Jim Buchanan actually mentioned this possibility in one of his earliest published articles (“Individual Choice in Voting and the Market ,” Journal of Political Economy, August 1954):
The individual in the polling place, by contrast, recognizes that his vote is influential in determining the final collective choice; he is fully conscious of his participation in social decision-making. The individual act of choosing is, therefore, social, even in a purely subjective sense.
The sense of participation in social choice may exert important effects on the behavior of the individual. It seems probable that the representative individual will act in accordance with a different preference scale when he realizes that he is choosing for the group rather than merely for himself. [p. 336]
(Later work on expressive voting by, among others, Geoff Brennan and Loren Lomasky , by Bryan Caplan , by Mike DeBow and Dwight Lee , and by Brennan and Buchanan  – and by Gordon Tullock in his own unique way  – more fully integrate non-material preferences in to public-choice scholarship.)
Here, though, I wish to make a point that likely has been made elsewhere but, if so, I’m unaware of. It is this: any change in motivation that a person experiences when moving from the private sector into the public sector (for example, when acting as a voter or when working as a government official) might move that person to become more other-regarding in his or her motivation. But it might not. In fact, it might have the opposite effect. It might make that person less other-regarding and more narrowly self-interested.
I recall the report that Barack Obama told then-Rep. Eric Cantor (R-VA), not long after Obama first took office as U.S. president, that “elections have consequences.” If the norm that someone works with tells that someone that democracy is all about letting the current majority do as it wishes, then it seems to me to be at least as likely that a voter will vote in accordance with very narrow material interests as he or she will vote with greater altruism. That is, if majoritarian democracy is about grabbing what one can if and whenever one is in the majority, then I see no good reason to suppose that any random voter’s motivations will be more other-regarding – or higher-minded – than are that same person’s motivations when he or she acts purely in a private capacity (say, as a business owner).
Because understandings of what democracy means and what justifies it differ greatly across different people, it is naive to suppose that any change in motivation that occurs when a person moves from the private to the public sector will necessarily be a change in a direction that every decent person regards as favorable. Moving a choice from the domain of private decision-making to that of public or political decision-making might change decision-makers’ motivations in a more favorable direction, but it might also change these motivations in a more predatory direction (“We won the election, so we get to take as much of your stuff as we like.”)