So why do the arraignment now? Or we can ask, why not?
The 'not' answer is that showing Sadaam locally seems a dangerous thing to do. It certainly could cause as much renewed support from those who support him (or who hate America) as it does relieve folks. It seems quite arguable that continuing to keep Sadaam out of view has clear advantages (why not continue to show pictures of him being captured and looking really bad, but not providing any new forum for his words or to show him looking better?)
On the other hand, why not try to get a bump in Bush's approval ratings by doing just what was done?
The Red Cross had warned that the US needed to hand over Saddam to the Iraqi authorities before 30 June, since otherwise the US would be in breach of I forget which conventions. They just about or almost met that deadline, perhaps to avoid yet another acrimonous round of reproaches and legal challenges.
By handing him over to the Iraqis, however, they necessitated the Iraqis to actually do
something with him, too. In fact, that was a win-win situation, since it afforded the Iraqis with a high-profile opportunity to show itself in an image of control - hey, a symbolic submission of the former dictator himself to their authority! Considering Saddam's continued impopularity in Iraq (perhaps the one single remaining comfort left for the Americans in the latest round of Iraqi polls
), it was also a way for them to score points with their population.
Anyway, thats just my superficial reading of it.