So I'm going to tackle another, related question: Why is there such a persistent, pernicious tendency to beat up on the poor? What psychological needs are filled by this all-too-common feature of our political discourse?
Now, it's very easy for undue speculation or pseudoscience to creep in whenever politics and psychology meet, so I'm going to be careful here. But here are a few reasons why Romney may have said what he said:
1. The in-group/out-group tendency. The division of the species into Us and Them comes very naturally to human beings, and it occurs at every level of human interaction, from middle-school cliques to nations to the sorts of civilizational struggles postulated by the Samuel Huntingtons of the world.
Romney was speaking to a very "In" group -- wealthy donors who had contributed $50,000 for the chance to spend an evening with him. What better place to highlight the differences between "us" -- hardworking, entrepreneurial, willing to play by the rules -- and "them" -- freeloading, entitled, seeking only to take rather than contribute?
2. The drive to dispel uncertainty. One of the more robust findings in psychology is that people greatly desire clarity. As the rumor researcher Nick DiFonzo told me last spring, "It’s hard to stay in an ambiguous mode and accept uncertainty," Whenever there's an event that lacks an easy explanation -- particularly a big, attention-grabbing one -- we'll do whatever we can to explain it, often using whatever cognitive tools are closest at hands.
Romney's comments are a prime example. While he's ostensibly talking about why Obama is popular among a subset of the electorate, the fuller context of his remarks has to do with the financial crash and sluggish recover of the U.S. economy -- massive, complicated events with many causes that interacted (and interact) in unpredictable ways. Cognitively, this is a nightmare. It's far preferable, from the point of view of the human brain, to come up with simpler, more straightforward causes. How about the fact that 47 percent of Americans are freeloaders (gasp!)? What easier way to explain why the economy is dragging? As an added bonus -- and this ties into the first point -- it's an explanation that was unlikely to offend anyone in the audience.
3. Confirmation bias. This one's simple: We're more likely to believe something if it jibes with what we already believe. On the right, the idea that the poor aren't doing their fair share, that they're freeloading and taking from hardworking Americans, has long anchored itself to the national discourse. (A great example is a ridiculously misleading chart that raced around the Internet a few years ago, which claimed that it was actually better to be poor than middle-class because of all the government largesse heaped upon the undeserving.) So this wasn't a new idea to Romney's audience. He was telling them what they had already heard, which only made them more receptive to hearing it again.
This also explains the specific interpretation of the 47 percent number. As David pointed out, discussions of who doesn't pay the federal income tax don't fully capture the situation, in part because it leaves out the payroll tax, which far more Americans pay. But to someone already predisposed to believe the idea that a big chunk of America is freeloading, "47 percent" will be the end of the story. There won't be room for much more nuance.
None of this is to defend Romney's comments, which were way off-base for the reasons David explained. Rather, it's to say that we can learn something about this style of discourse by framing it in terms of universal psychological drives and tendencies. The idea that the poor are freeloaders may be false and unfortunate, but it flows directly out of many of the biases that define us as human beings.