You cannot get people to change if they don't want to. All it does is put up a big banner saying, "rules lawyers welcome". You know this.
And then we can ban them. But not before.
Most people here seem to have forgotten, thankfully, but at one point my usual contribution to politics threads was along the lines of "Whoo anarchy, down with [ruling party of country under discussion], fuck tha police". Usually worded very mildly, it's true, but the sentiment was there. I have since learned, both in terms of my views themselves and in terms of when it is appropriate and constructive to express them. People can change.
Debate is adversarial by nature, but it can be civil — both (or all) sides are trying to 'score points' by undermining the other guy's position or reasoning, whether formally or not. The emphasis is less on sharing information and more on 'winning'. Debates are where the fallacy-dropping starts showing up — after all, in a debate, using a fallacy is only bad if you get caught. And conversely, when someone starts fallacy-dropping, it's a pretty good indication that they're treating the thread as a debate. If everybody knows it's a debate, there's no problem. A problem arises when 'debate' is mixed with one of the first two types.
Then I think I have been misusing the term debate, because this sounds like what I would describe as "debating badly" or "debating dishonestly". In a debate, to my mind, both parties should be trying to convince the other through the use of arguments they sincerely believe to be correct (in the case of devil's advocates, the arguments themselves should be valid even if they don't agree with the conclusion), otherwise it's a foolish and disingenuous exercise. Both should be open to the possibility of learning from the other, and neither should see it as a competition that can be "won". The aim should be to be right, not to appear to be right.
Also, though, I think it's very easy for a discussion, as you define it, to become heated quite naturally, even when only two people are participating. For example, suppose Alice
are having a discussion, and Alice is sincerely interested in X:
Alice: But why is X so great?
Bob: Because FALLACY.
This is a polite discussion, but depending both on how Alice responds to that fallacy and how defensive Bob feels about X, it could turn nasty very quickly.
And these would not be formal rules, but just part of the general "culture" of the forum here. If a thread didn't adhere to any of this, the rest of us would be empowered to remind the participants of what the expectations are, perhaps by linking to a page that contains a summary of whatever consensus we come up with here. After that, any thread that didn't go along could be avoided by those of us who want to participate in threads with a clear purpose and a sense of a genuine exchange of views.
This was actually my intention from the start, hence my use of the word "guideline". These wouldn't be enforced rules as such, but advice on how to behave civilly and rationally (and hopefully reduce the need for any mod enforcement of the actual, existing rules).