A very good idea, @timcliff. Upvoted and resteemed!
I suggest that we have a certain form for 'discussion' posts. For example:
1- The creator of the discussion post should not state his/her point of view in the post itself. The post should be for opening the discussion.
2- Anyone (including the author) who wants to defend one side, must state the side he is choosing at the top of the comment. Then, he should state his argument (why he thinks it is the right side).
3- Top-level comments should be reserved for new arguments. Refuting or supporting any reasoning should be through a response to that comment. You can not refute other people's ideas on top-level comments, only replies.
4- If you agree with an idea, you should upvote it. If you disagree, you should downvote it. a Down-vote should not be considered as an offense in discussions. It is only an expression of agreeing or disagreeing.
It's an interesting proposal. I like it, but it might be very difficult to get people to conform to a specific format when the community is decentralized like it is. Also, the idea of downvoting over disagreement is quite controversial. It may actually be a good topic to open a #discussion about ;)