All the other answers are the traces of an informal and unproductive debate. Strong opinions will lead to controversy; personal attacks will lead the debate to an argument; An unlimited speaking time will lead to the possibility that a party to the debate abuses its speaking time and does not let the other party speak.
establishing rules and guidelines is the answer
To be a formal debate, the debate must include established rules and guidelines. ;3
A debate is a statement of an argument. A formal debate takes place between two opposing parties. Each side must have a proposition and they argue against each other to prove the other wrong. It must have an affirmative assertion and a counterclaim.