Both Stoat and Rabett(or Eli's Brian)have again weighed in on the topic of the motivation of the global warming skeptics. Brian is closer to the mark, I think, but William, not so much. William says it's because they can't understand the science, while Brian ties it to politics and economics. The fact is, the number of people who understand the science in detail is tiny - many of the important details are hidden in models so complex that even those who run them may only understand parts in great detail. Other branches of science have the same problem, but rarely to the same degree.
My exposure to a group of skeptics has convinced me that many of them understand much more than your typical sign carrying climate warrior. Their combination of knowledge and attitude makes them good at seeing through many of the oversimplifications and exaggerations common in the press and even heard sometimes from distinguished climate scientists. They know some crucial truths: that temperature and CO2 have been quite a bit higher in the past, that the connection between storms and AGW is somewhat uncertain, that large uncertainties exist in climate feedbacks and climate cycles.
Of course they also believe many things which are almost certainly false: that the planet hasn't warmed since 1998, that the planet (rather than just Greenland) was 6-8 C warmer in the Eemian, that the lag between CO2 concentrations and temperature during glaciation events proves that CO2 changes are an effect, not cause of warming, some oddities about the temperature structure of Venus and more.
The usual AGW soldier has no clue as to how to deal with either of these types of "information" and that gives the skeptics confidence. Ultimately, though, I think that their opinions, like those of many on the other side of the debate, are ultimately tribal. Their tribe is conservative, often religious, deeply distrustful of anything requiring international cooperation. One consequence of this analysis is that those who deal in insults strengthen them far more than weaken them. Insulting the tribal flag causes the tribe to rally around.
In my by now somewhat regular meetings and debates with my skeptical friends, I try hard to listen and (usually) disagree politely. They give me at least equal courtesy. I don't expect to persuade many or even any, but I find the dialog useful anyway. Contrary to what William found about skeptical blogs, many are willing or eager to talk amelioration and policy.