This doesn't protect someone (or a whole society) from bad actors who know how to exploit the assumption of positive intent. This might work for arguing with Aunt Tillie at Thanksgiving dinner, but it's a loophole actively exploited by people in power whose motives run counter to what's good, in general, for society as a whole. See: tobacco executives, climate change deniers, those who profit off anti-vaxx sentiment, televangelists, etc.