The problem here is there's no way to figure out the "spirit" without having followed a rather extensive history - and the fact that the same justifications are repeated every time the rule is questioned in any way is testament to your already realizing that.
Why not just have the rule say what's actually meant, instead? If the desire is "no replies that are or might spark a controversy", then it's clearer for the rule to say that, instead of the vague, terse prohibition on complaints.
Better yet, go all the way and forbid replies entirely. That achieves the same stifling of conversation, in this one context where it's deemed "terrible", without the enforcement that can seem capricious and arbitrary (as you say yourself, "it's often not easy to tell the difference") and can needlessly shame an otherwise well-intentioned commenter.
Keeping it terse and relying on "spirit" is an excuse to maintain that aribtariness.
Why not just have the rule say what's actually meant, instead? If the desire is "no replies that are or might spark a controversy", then it's clearer for the rule to say that, instead of the vague, terse prohibition on complaints.
Better yet, go all the way and forbid replies entirely. That achieves the same stifling of conversation, in this one context where it's deemed "terrible", without the enforcement that can seem capricious and arbitrary (as you say yourself, "it's often not easy to tell the difference") and can needlessly shame an otherwise well-intentioned commenter.
Keeping it terse and relying on "spirit" is an excuse to maintain that aribtariness.