I left a six-line comment on the main site suggesting that a user slightly modify her or his question-posting behaviour. As a response, the user asked me to open a meta thread to discuss non-mathematical issues, without addressing my concerns. I hadn't actually intended to discuss; I was hoping that simply making the suggestion would make the user aware of the problem I saw and hopefully motivate her or him to follow the suggestion. I said as much in a response and asked whether I should take the response to imply that the user doesn't intend to follow my suggestion; I didn't get a reply to that (yet), which seems to imply an answer in the affirmative.
I'm wondering how to respond to such a situation. On the one hand, the user is quite right that the main-site comments shouldn't be used for extended meta discussions. On the other hand, it seems rather likely, given previous discussions, that the result of bringing this up on meta would simply result in others agreeing with my suggestion, and I don't want to waste everyone's time doing that; or, more to the point, I don't want to let the user's refusal to engage with my suggestion force me to waste everyone's time. But again on the other hand, I can't just tell the user that I'm right and there's nothing to discuss because everyone agrees with me, since the behaviour isn't exactly the same as was previously discussed and my prediction that others will agree with my suggestion is merely an extrapolation from the previous discussions.
I'd welcome any suggestions on how to deal with this situation while attaining all three objectives of not clogging the main site with meta discussions, not wasting everyone's time with an unnecessary meta thread, and getting the user to modify her or his behaviour (or else being persuaded that there's no need for that).