"Curveball" and WMD claims

The Guardian story makes it absolutely crystal clear that the Iraqi agent named "Curveball" could not possibly have succeeded in convincing American intelligence that Iraq possessed WMD unless the Amercans were fully prepared to believe such claims. Such phrases as:

The commission concluded that Curveball's information was worse than none at all. 'Worse than having no human sources,' it said, 'is being seduced by a human source who is telling lies.'
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It now appears there were problems with Curveball from the start, but the intelligence community was willing to believe him 'because the tales he told were consistent with what they already believed.
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While the results were inconclusive, a US official was surprised to find Curveball had a hangover and said he 'might be an alcoholic.'
(emphasis mine)

These are not phrases one uses unless one is describing an agency that was in an extreme state of credulousness. And why would they be willing to be so gullible? Let's look at this passage:

[Curveballs] information was central to an October 2002 National Intelligence Estimate that concluded Iraq 'has' biological weapons, and was widely used by President Bush and Dick Cheney to make their case for war.

People have previously noted that the NIE was widely used to justify the Iraq War, but that Cheney first began hinting at the "necessity" of going to war with Iraq as early as July 2002 and that Bush made a speech to the UN in September 2002 that purportedly made the case for going to war (My own personal estimation at the time was that Bush's speech didn't justify the death of a single person, American or Iraqi, solder or civilian My feeling afterwards was that "If he had a case to make, that was the time when he would have made it."), but that the NIE wasn't produced until a month after that. George Tenet, being a good bureaucrat, rather obviously decided that he had better get with the program and produce a National Intelligence Estmate that backed up what his bosses were saying.