It is true that water vapor is the strongest greenhouse gas. However, that's certainly not the entire story. It is also true that it is carbon dioxide that is upsetting the balance in the Earth's ability to regulate itself. As humans pump more and more carbon dioxide into the atmosphere while simultaneously cutting down huge swaths of forest (and thereby harming the Earth's ability to scrub carbon dioxide), the Earth's ability to cool itself is significantly reduced. As this process accelerates, the ice caps melt, releasing more water vapor into the atmosphere via evaporation, further compounding the effect caused by unregulated carbon dioxide emissions.
This all adds up to an accelerating snowball effect that by the end of the century could see average global temperatures increase by six degrees Celsius. That means no more year-round snow and ice on the polar ice caps, sea levels meters above "normal" and a whole host of problems for flora and fauna (us) alike. The science is in, and the denialists are endagering us all.
This is a classic case of Pascal's Wager, except that in this case it is actually a good argument. If we do nothing and anthropogenic global warming (AGW) is real, we risk the end of civilization as we know it. If we take aggressive action and AGW turns out to be hogwash, then we'll have taken long steps toward cleaning up our environment: a net positive for many reasons unrelated to AGW, including reduced loss of habitat, healthier oceans (and fisheries), and fewer pollutants in our food and water. Why some people insist that we should continue to rape our planet as we've always done seems, in this light, grossly irresponsible and short-sighted.
I should add that AGW denialists are in the same camp as creationists because they willfully disbelieve science they do not understand so that they can rationalize closely held, pig-headed beliefs which only serve to preserve the status quo. Change is often hard and uncomfortable; even costly. But that doesn't mean we shouldn't embrace it. Read some ACTUAL science instead of letting people with an agenda spoon-feed you lies.
