If Obama is scared to have a discussion with McCain, how can he possibly meet with world leaders like Chavez, Putin, or al-Assad?
For real debates, each candidate should be allowed to select some people who will ask the other candidate questions. They should be encouraged to select people who will ask hard questions and be tenacious, but not vicious or discourteous. As you note, if the President can't stand up to that, he won't stand up to the country's enemies.