I don't see how a single thread could work, honestly. There are so many different topics and issues that could be covered in a debate forum (or sub-forum) that a single thread would feel either like too much of a clusterfuck or too closely centered around a single topic. I think that having a subforum for Serious Discussion, Debates, and Current Events would work well. The three together allow for more than enough different topics as long as people post there. And if they don't, it'd be simple to remove.