A few things about Congress and their latest report that Iraq didn't have WMD:
We know Iraq had WMD; they used them dozens of times.
Powell played phone intercepts to the UN that Iraq was moving stuff out the back door when the UN showed up at the front door. He also played intercepts of instructions to Iraqi soldiers to delete all references in documents to nerve gas.
I find it impossible to believe that every single intelligence agency on the face of the planet was wrong about Iraq and WMD.
As to your question - why does Congress lie? Congress has lied in the past and will lie in the future. The CIA does get stuff wrong for the same reasons Congress gets stuff wrong.
No one wants to be the one to go out on a limb and make a decision or deduction that can come back to bite them later so when conventional wisdom says Iraq had WMD, they agree. When conventional wisdom says Iraq didn't have WMD (because we haven't found them yet), they all agree.
I agree.