1. Spend any time at all reading comment wars on climate blogs (example here is from an AGW-friendly blog but there is no monopoly on bad manners) and you will be appalled at the personal and spiteful tone. Clearly the disagreement is not just about science.
2. In a chaos-rich situation like the stock market or climate modelling, people can find data that fits their hypotheses, can build models that fit their preconceptions, and have some success and find plausible reasons for failures, regardless of whatever their position is.
3. Arguments are available at every level, from the validity of current temperature measurements, through whether the earth is warming and if so, at what rate, to whether the warming is unusual, to its possible causes, to whether anything can be done about those causes, to whether anything SHOULD be done, to the costs and benefits of preventive action vs adaptation.
4. On one extreme, it's the future of the planet that is claimed to be at stake. The opposite extreme claims that human freedom itself is at stake.
5. There are well-meaning, serious, sincere people on both sides of the debate. There is also contempt and deep mistrust about the opposite side.
6. My own biases favor doing nothing about CO2, but plenty about pollution; nothing about carbon trading, but plenty about economic opportunities and fair trade for emerging economies; nothing about UN or NGO empowerment but plenty about accountability to substantiate claims made about benefits and risks.
Above all I favor improving the quality of the debate and the transparency of the underlying information. This marks me for some AGW types as a member of the loony right, sold out to industrial interests and uncaring about 'the biggest threat mankind has ever faced'. But in any matter as important as this is claimed to be, where any useful response requires unprecedented economic sacrifice, why would anyone do otherwise?