It seems the core of both discussion and debate is the dialogue. Two or more people conversing about a topic, considering what one another are saying, making compromises on definitions,... it's nonfiction writing, where your audience is able to give you near-instantaneous feedback.
The difference between a discussion and a debate is the depth of feedback. In a discussion, the audience wants to figure out what the writer is saying. "What does this mean? Can you reduce that paragraph to a word? Can you give an example?" You ask these sorts of questions, and generally assume that the writer is competent enough in that field to take the role of instructor. It's a bit of pressure, but for clarity's sake. (The competency is not only expected of the opening poster, but also of anyone who posts... if you say something in a discussion but someone doesn't understand, you are a candidate for their questions.)
A debate brings in something a lot heavier than clarity. It brings in truth. Everyone wants to have a true picture of the world, and many people who have false pictures of the world will still argue as though their view is accurate. Luckily, there are many ways to find out if something is false (far more than there are of finding out if something is true). You can look for persistent fallacies, contradictions, and so forth. You make sure the definitions are clear, and that the arguments flow a to b to c. Although you are unlikely to find the truth in any given debate, you are very likely to come across pitfalls and falsehoods. Personally, I like to continue doing research after the debate ends. "Next time, Gadget! Next time!"
Apart from things like spam and trolls, which clearly don't belong, I don't think that rants really fit here. It's "zero feedback". Without the meaningful dialogue, it's missing half of the writer: the audience. Rants, fiction or non-fiction, might be better suited to the Writing section of the Creative Realm or the Main Lobby. Same with the sharing of anecdotes (unless you could theoretically interrupt show-and-tell to poke at the topic with a stick): fireside stories seems like more more of a Main Lobby sort of thing.
The deciding factor, I think, is the question:"is there room for discussion or debate?" If someone could theoretically give you feedback on your rant, then it can fit.