Here's what I think...

In-person debates are somewhat pointless, because someone can simply start lying their ass off and you won't be able to do the research in time to call them on it. Even if you know what they're saying is flat-out wrong, and you call them on it, your opponent can simply accuse you of being the one who has the facts wrong - and an audience that doesn't already know the truth won't have any way to tell the difference. The only kind of debates worth having are written debates.