You can constructively tell someone their work is not up to the standard required, and not accept mediocrity. You don't have to be rude or uncivil to do that.
There seems to be a need to for continual escalation of feedback until it is processed. Often times this processing doesn't occur until they are uncomfortable, or as in the case of family, tired of listening to you!
Then phrase it another way until they do, or otherwise find a way to communicate it that makes the issue clear. That's still not a reason to become hostile or toxic, or berate or denigrate someone.
And bringing things back to the article we're commenting on, here: it doesn't actually look like that happened at any point here. Despite how the person in question self-described themselves, it doesn't seem to me that they actually behaved in a problematic way. It's perfectly reasonable to offer precise, to-the-point, clear criticism. None of that requires being rude, uncivil, or unconstructive.
The comment I was replying to said '"Constructive" feedback only goes so far.'. I emphatically disagree; the article talks about a ten-page letter full of what sounds like highly constructive feedback.