Why not just say what you mean, instead? If the desire is "no replies that are or might spark a controversy", then why doesn't the rule say that?
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.