Some folks are ill-mannered. Some folks can turn any thread, on any topic, into a sewer. Some folks exercise that ability regularly.
The "academic thread" proposal would only work if those who disrupt it face meaningful consequences. Given the behaviour we have all seen on open threads, the academic thread would require a very heavy-handed moderator. No matter the original topic, we're discussing religion here ... things are interconnected, and even valid discussion in good faith will drift. Deciding what comments are valid drift, and what comments are "goat blood" material will require much more intensive moderation than the simple "don't make it personal" rule.
If the mods are willing to take up that burden, of course, the system could work. But let us have no illusions ... it will be a big burden.
The problem as I see it is that we are operating under the assumption that many on the open threads actually desire an honest and this assumption is erroneous.
What I see on most open threads are a half dozen or so lies, that have been proven to be lies countless times, reworded in the gleeful hopes of some “gotcha” moment.
I don't. It's fine that people have an outlet where they can let their hair down and argue in whichever low-brow style they like, within very broad set of rules.
But it would also be great to have an environment where polemics are robust, but there is more light than heat.
I would say, if a rule is difficult to enforce without the Moderator constantly on top of it, let us drop it. For example, if topicality rule proves impractical, it should be relaxed till it becomes practical. But the sourcing rule and substantiality rule are not hard to enforce. We should seek rules that are simple.