I think creating some rules (let's call them guidelines?) would help to lower the temperature as well as structure the debate. Though each guideline may seem trivial in isolation, every little helps (as the old lady said when she peed in the sea). There, that's a guideline to continue
@Heyo's excellent start. Inject humor when things seem to be getting too serious. And another. Don't forget to compliment what you see as good arguments as well as criticize bad ones.
It's all about lowering the temperature. Here's another.
Don't reply to posts with a single word ("rubbish"), or short sentences ("that's nonsense"), or emoticons (
), with no explanation as to why you think that. It's the equivalent of turning your back on someone that speaks to you and refusing to acknowledge any further communication. It would be considered very rude IRL and tends to make the recipient angry, which is the real problem. If you don't think the post merits a response, don't reply at all.
OK. I'm trying to start a list here. I'll set them all out and invite additions. By the way some good suggestions have already been made. Feel free to add them anyway. Remember the objective of the guideline is to lower the temperature of the interaction, not to simply improve the quality of the debate.
1. Answer the question.
2. Inject humor when things seem to be getting too serious.
3. Compliment as well as criticize.
4. Avoid put downs with no explanation.