You keep saying “imaginary”, but microagression is about what has been said, not relevant to dwell on what the person might have wanted to mean.
You keep coming back to this perceived paranoia: “as if people are secretly trying to hurt you”. This is not what this is about. This is people that got hurt, and no matter what others are trying, secretly or not, that hurt is better be documented.
It doesn’t mean that someone ought to be punished right away for each comment deemed offensive by anyone. It’s just that these occurrences might be relevant later on and if they’re not documented, it’s gone.
Documenting all offenses is a good idea for people who are at risk of finding themselves needing that later. And if you don’t think this happens frequently enough, you haven’t been paying attention.