We don't know what we think about a lot of issues – hardly a novel finding, dating back to Converse. What's even more problematic is how badly we misjudge what others think, which is a fundamental component of how we form our own opinions and orient ourselves toward society.
A real psychologist might disagree here, but political psychology evaluates judgment and decision-making under the assumption that much of human cognition is "hard wired" for basic survival functions and is quite poorly adapted to understanding abstractions like politics (see Kuklinski & Quirk, Reconsidering the Rational Public: Cognition, Heuristics, and Mass Opinion). In other words, our thought processes are geared toward self-preservation, including bolstering our self-image. This is part of the reason why having a low self-image is recognized as a medical condition. The "normal" mind excels at convincing itself that it is correct even when it is very, very wrong.
One of the tricks our minds use to make us feel better about the decisions we make is to convince us that others share our opinions. It is common in the absence of other information (and perhaps even despite it) to believe that the majority of our fellow citizens believe the same things we do. If I am against capital punishment and don't know anything about public opinion on that subject, I will guess that a majority of the public is also against it.
This, I believe, is one of the main culprits explaining survey results like these:
Virginia Commonwealth University Life Sciences Survey. May 12-18, 2010. N=1,001 adults nationwide. MoE ± 3.7
"From what you’ve heard or read, do you think the evidence on global warming is widely accepted within the scientific community, or do many scientists have serious doubts about it?"
Widely accepted: 37% Many have serious doubts: 49% Unsure: 14%
ABC News/Washington Post Poll. Dec. 10-13, 2009. N=1,003 adults nationwide. MoE ± 3.5
"Do you think most scientists agree with one another about whether or not global warming is happening, or do you think there is a lot of disagreement among scientists on this issue?"
Most agree: 36% A lot of disagreement: 62% Unsure: 2%
Your gut reaction is probably that this is the media's fault – too much Glenn Beck, too many effective disinformation campaigns by denialist groups and professional "skeptics." But these are objective questions, namely about the scientific consensus. A five-second google search would reveal that 90%+ of climate researchers subscribe to the climate change hypothesis. Even denialist arguments on Fox News don't have the audacity to claim that a majority of scientists have serious doubts; in fact, the small minority status of the Skeptics is often played up to fuel the right's latent martyr complex. If we had the information we would probably answer the question accordingly. Lacking that information we just assume that everybody else probably believes what we believe, namely that global warmin' is nothing but a big pinko conspiracy to take away our Dodge Durango.
It is regrettable that we use our own opinions as a proxy for the majority so often given how sorely misinformed we are most of the time. But if I feel that it's regrettable, then surely most people do. A collective solution may be just around the corner.