Can there be comments which are legitimate but nevertheless also predictable, unthoughtful, unsubstantive? Sure there can. We don't need those here. They don't affect threads in a good way.

Can there be comments which are illegitimate, but nevertheless manage to be thoughtful/substantive/unpredictable? Surely this must also be possible. Such comments could well make for interesting conversation, in which case they'd be fine.

There's no rule requiring commenters to be right (which is handy, since to a first approximation we're all wrong about everything and rarely have any idea what we're talking about—this is what they used to call "the human condition"). When people approach conversation with a strong need to be right, that doesn't lead to curious conversation, it leads to the situation in the famous xkcd classic.

I'm not saying that the truth doesn't matter and certainly not that people should just bullshit. Bullshit is a lot less interesting and more predictable than it assumes it is. I'm saying that an open-minded, exploratory, conversational way of looking for the truth yields best results here, and trying to categorize things as legitimate vs. illegitimate isn't in that spirit. As for "legitimate denouncements", god help us, that covers every denouncement ever made, as far as the denouncer was concerned.