I think you’re right that the initial blog post is repeatedly making a big mistake: running into a values difference and using the mood argument as evidence against the position.
I think to turn this into a useful heuristic, the patch is to reverse the order of operations. If you go from Noticing Missing Mood → Be Suspicious you can easily used this to tar your political opposition. But if you go from Intuition of Suspicion → Look for Missing Mood, it can be a highly productive heuristic for determining what seems to be wrong with someone’s argument, whether or not that actually makes it wrong. You can immediately find cruxier issues between you and your political opponent (like the values differences above). This post seems to do that well.
Doing this on your own beliefs is arguably the most productive! “Huh, shouldn’t I also feel sympathy towards the people my proposed policy hurts?”