Look, Carville has a sharp tongue but this one goes beyond the bounds of a decent intra-party race between two candidates. So why did he say it and, more importantly, why did he reiterate the point (confirmed that he MEANT exactly what he said and that he was not taken out of context)?
Note that he went on to say that he is only a "periphery" player in the Clinton campaign and that he was speaking "his own opinion". Well, sure, it's so outrageous that the campaign has to distance itself from the comment. But no one in the Clinton campaign (let alone the witch) came to Richardson's defense.
So here's what I see - Hillary's own way of playing the fear card. Several prominent Democrats have now come out and endorsed Obama. But there isn't exactly a flood of Hillary defections. So I believe Richardson was intentionally and specifically targeted as the guy they would smear for one reason - to send a message to the probable hoards of others (many of them former members of the Clinton Administration or, at the least, beneficiaries of 8 years of Clinton Presidency). She's trying to cower others into withholding their support for Obama. Other Dems have to at least ask themselves, "if I now endorse Obama, does the Clinton machine attack me for it"?
It makes sense in a GOP, Karl Rove, sort of way. And Hillary and Attack Dog Bill are looking more and more like EXACTLY THAT. From Bill's statements likening Barack Obama to Jesse Jackson, to "SHAME ON YOU", to the picture of Obama in African garb, to jumping on the Reverend Wright "controversy", to Bill's "it would be nice to have two candidates who both love the country" - it's Rovian in the fullest sense and, thus, would be highly unsurprising if the attack on Richardson was NOT orchestrated at the highest level of the campaign.