Ordinarily, I admire people who tell pollsters they "don't know" the answer to some poll question. And I'm often amazed by how few of them there are, because for many poll questions, "Don't Know" is the only correct answer. For example, there are questions asking for predictions about the unknowable future: Will newspapers survive? Will there be another terrorist episode in the United States in the next year? Will the Tea Party be a force in the 2012 election?
Then there are questions that require expertise to have even a coherent opinion about them--let alone the correct one. Are we headed for a double-dip recession? Is the hot weather this summer a sign of global warming? This is not meant to be patronizing. Nearly everyone has expertise about something-or-other that even Paul Krugman may not share. But people seem happy to answer pollsters' questions on any subject that is thrown at them.
However, I am depressed rather than impressed about how many people say they "don't know" what President Obama's religion is. Weirdly, that number is rising. It was 36 percent of the population in a Pew poll in March, and has risen to 43 percent in August. If you believe this poll, in other words, at least seven percent of the American population used to know what Obama's religion is, but have forgotten.