This is a good policy, if followed by people on all sides, to enable a pleasant dialog without losing the ability to refine and dispute ideas.

However, arguments aren't any less valid if presented in an unpleasant way, or if there is a mix of "nuh uh" and meaningful and substantive statements. Furthermore, if someone else is approaching an issue from a very different perspective than one's own, it might be difficult to distinguish an elaborate, wordy "nuh uh" from a meaningful and substantive statement. It might take some dialog to even be able to tell the difference, especially in cases where terminology differs between different people. For example, "racism", "patriarchy", "woke", etc. can mean rather different things to progressives and to (select) alt-right-leaning types. Even if both are bright people and intend to convey their insights in a productive way, they might not initially recognize what the other is saying, and so a meaningful and substantive point when interpreted using the others' vocabulary would turn into elaborate and wordy nonsense, and hence an apparent "nuh uh".

So then the questions are: what does one do in such cases, and how does one tell?

If I had infinite time, which I do not, I would reply calmly, meaningfully, and substantively to responses that might possibly be one of those cases, or which might possibly be converted into one of those cases, because the most important insights that I'm missing are most likely to come from the most different perspectives than my own (as long as they are still grounded in logic and evidence).

As a practical matter, I reply to most everything anyway, though not always with all three of those qualities. I don't think I could successfully argue that this is the optimal concession to limited time, however.

What is your ideal and practice in such cases?