Goldman's CDO Investors - were they stupid?

The CDO product at the center of the SEC's case against Goldman Sachs raises the question: were the 'sophisticated' investors (including ironically the middleman Goldman Sachs) that bought into this transaction stupid or victims (or both)? Leaving the legal and factual arguments for the moment out of the discussion - what was the motivation that caused the fund managers at IKB and ABN Amro to buy securities that were one or two steps removed from any real underlying economic transaction? Speaking from experience I can see them as busy, maybe even diligent people who were working in a set of parameters that prevented them from questioning certain assumptions at the heart of the structured product business: that securitised products contain what the label promises, that companies with a certain public image behave in a way that confirms this image, that all players on the field can be trusted to pursue goals that do not harm the other participants.
Securitisation in particular is critically dependent on trust as the buyers in effect must give a certain amount of leeway to the creator of the product they are purchasing. The whole business idea underlying securitisation is the fact that the buyer does not want to - or is not able to - to buy the underlying assets himself. In effect, he buys a packaged product and can never expect to fully analyse all the assets - would he do so he could as well purchase these assets directly thus disposing of the need for securitisation.