What leads to flame wars? Why do people at comp.os.linux.advocacy spew so much venom at each other, arguing in favour of either Linux or Windows?

The reason is that each camp is absolutely certain that it is right. Such certainty makes these people view anyone with an opposite opinion as having an ulterior motive or agenda (and not just some legitimate grievance). It then becomes a battle between Good and Evil. The moment this happens, all the rulebooks are thrown out; Good has to eradicate Evil; there can be no two opinions about this and no need to think rationally and conduct a logical argument for the position adopted. I will not go into the reasons why people are so certain of their beliefs; a lot of factors are at play here, like faith, personal values, belief systems and so on (in some cases this belief might even have a strong factual background -- in which case the rage felt against the opposing camp will be even stronger!).

In the case of political issues, we have wonderful leaders who do nothing to calm things down, but rather play on these emotions and keep the pot boiling, instead of taking a level-headed and rational approach. Someone who does not bow to the populist pressures is vilified as having given in to the other side's pressure and is either goaded into action or is pushed out of the picture altogether. In this age of fast food and soundbites, nobody has the patience to spend the requisite time to analyse a candidate's platform and judge for themselves whether what he says makes sense. Add to this the inherent complexity of economics (quick, tell me whether a stronger dollar is a good thing or not, keeping in mind that we need to boost our exports, while not allowing our domestic industry to languish because importing capital goods is more expensive), and the ability of governments to indulge in fancy bookkeeping that hides the true state of affairs as long as they are in power, and a citizen's efforts at getting the real picture are pretty much doomed.

Whew, what started off as a socio-cultural commentary somehow morphed into a political rant!