What evidence is there that people care about the social planner’s objective function except insofar as it affects material allocations? The most apparent evidence is the energy that economists and others devote to studying such questions, revealing that somebody (either the researchers themselves or those who fund their research) cares about the answers...
It is no use to respond that these moral arguments are mere smokescreens that disguise the real material motivations of those who fund our investigations. For why should such smokescreens be at all effective unless there is an audience that cares about moral issues? The “smokescreen” response denies the moral motivations of one segment of society but must attribute similar motivations to a different segment.
Indeed. It's striking how quick people are to assume that their political opponents (and even their allies!) are just pretending to take morality seriously. There are some cynics out there, but they normally avoid moral argument, rather than engage in it insincerely.
If you think that no one could sincerely hold the moral views they claim to hold, you should try to convince someone to abandon their religion. After a few hours, you'll probably have every right to doubt their rationality. But if you think that "it's all an act," you're just being paranoid.