This. The whole "they'll riot anyway" line of logic is completely faulty. The "Dry" VEISHEA back in the late 90's, after that guy got killed, was a super unpopular decision. No riots, though. 2005, like you said, was tame.
That said, if Leath cancels the events planned for this weekend, then there might be some folks who still want to go nuts, but I'm guessing the police will be out in force, and put to bed anything before it gets out of hand.
How did a dry VEISHEA work? Did they not sell alcohol in Ames and shut down the bars?