John Stuart Mill recommends the adversary system for the court of opinion as well as for courts of law. In On Liberty Chapter 2 “Of the Liberty of Thought and Discussion,” paragraph 39, he writes:
I do not pretend that the most unlimited use of the freedom of enunciating all possible opinions would put an end to the evils of religious or philosophical sectarianism. Every truth which men of narrow capacity are in earnest about, is sure to be asserted, inculcated, and in many ways even acted on, as if no other truth existed in the world, or at all events none that could limit or qualify the first. I acknowledge that the tendency of all opinions to become sectarian is not cured by the freest discussion, but is often heightened and exacerbated thereby; the truth which ought to have been, but was not, seen, being rejected all the more violently because proclaimed by persons regarded as opponents. But it is not on the impassioned partisan, it is on the calmer and more disinterested bystander, that this collision of opinions works its salutary effect. Not the violent conflict between parts of the truth, but the quiet suppression of half of it, is the formidable evil; there is always hope when people are forced to listen to both sides; it is when they attend only to one that errors harden into prejudices, and truth itself ceases to have the effect of truth, by being exaggerated into falsehood. And since there are few mental attributes more rare than that judicial faculty which can sit in intelligent judgment between two sides of a question, of which only one is represented by an advocate before it, truth has no chance but in proportion as every side of it, every opinion which embodies any fraction of the truth, not only finds advocates, but is so advocated as to be listened to.
The problem I have with this in practice is that it doesn’t work well if too large a fraction of those in a discussion take the role of intensely partisan advocates and too small a fraction take the role of relatively nonpartisan judges. That is, if there are too few “calmer and more disinterested bystanders,” the adversarial system in public affairs cannot achieve the effect that John Stuart Mill hoped for.