Whether or not its a good idea to announce one's rationale for upvoting has nothing to do with whether authors should show or tell. Phrases don't apply equally to all situations the words could fit in. There are reasons why people recommend that to writers and they aren't at all the same reasons people recommend that people up/downvote silently, as they are almost completely dissimilar situations.

It seems to me that the problem with the post you are replying to is that it dismisses a post as mostly garbage rather than its defiance of good writing practice.

So is this phrase ripped from its homeland just to gently shush someone being rude? I suppose It also has the effect of implying that the norm of upvoting stuff you want more of is implicitly assumed. The irrelevance of the phrase could even be a plain old "passive aggressive" gesture that not only is the comment it was replying to so unwelcome something should be said, it's so unwelcome it does not even need to be said well.

Or maybe people just liked the way the popular phrase could also work here?

Is it rude (or some other bad thing) of me to post these thoughts?