They don't undo science that is 150+ years old.
Mistakes happen in science, just like any human endeavor. Remember the years-long debate, in the early 2000s, over the satellite measurements of John Christy and Roy Spencer? This was a fine fight over the details, though it mostly took place before the era of blogs. Eventually Christy & Spencer found an error in their calculations, they corrected it, they admitted that their satellite was showing warming at about the expected scale, and everyone moved on.
It was too their credit that they admitted their error. It hardly made them devils. It didn't prove that all skeptics came from the dark pits of hell.
And it's no different now. Mistakes happen. It'd be nice if they didn't, but they do. Everywhere.
Still, things could definitely have been handled differently. Phil Jones should not have denied those FOIA requests, and he's paying the price for that. Pachuari should not have ignored glacier data, though I'm not sure he did. Someone in his position, two months before the Copenhagen conference -- I'm sure he was utterly inundated with requests and information. He is human. Things slip. The human capacity is finite.
But carbon dioxide is still a strong greenhouse gas. Even small amounts of it warm the earth. This science is over 150 yrs old, and can easily be shown by anyone with a gas chamber and a light source.
Basic physics shows that a small amount of CO2, ~280 ppm, warms our atmosphere by 7-9 °C. So why shouldn't another 35% lead to even more warming?
Let's not get lost in all details (like they want you to). Just because some scientist in Korea cheated on is stem cell data does't falsify the Krebs cycle. And that's where we're at.