I would shy away for moral topic people get all wound up about i.e.(abortion, terrorism, etc) I would choose a fun topic that is light hearted, like why dogs are better than cats or why waiting to the last minute to do things is better than spending weeks planning them out. This will also let you be more comfortable becuase the idea will more likely be your own and you will be a subject matter expert on why the ps3 is way better than the xbox360.
Good luck