The simplest debate or cause of friction can lead to havoc in the right environment.
Arguing over a scarce seat is what did it at Comic-Con when two patrons tussled to the point where one stabbed the other in the eye with a pen. View story at http://www.usatoday.com/life/2010-07-24-comic-con-stabbing_N.htm
Other sources of friction could come from competing researchers in too tight of proximity or a disparaging word about someone, their work or their institution. Reputation is an important asset in academia and slights are not easily ignored.
And although we are long past the era of the Scopes trial scientific research is constantly propelling forward and at times pushing along those social, moral and religious hot-button issues.
So identify where hot button issues or presenters have a greater chance of occurring and plan appropriately, whether that means a security guard near the lectern or an opportunity for participant responses at the end of the event.