And it's not just because creeping condescension is often a component of how people formulate comfort. By that I mean statements that in often more subtle ways take the general form 'this problem is no big deal'.
Such replies are invalidating of both the problem and the distress the problem is causing someone.
More generally, in a forum like this where posts are read by both those who are ill and those experience the illness of another, a really good supportive post somehow navigates a narrow space without invalidating either side. We live in a time when advocacy deeply divides politics and it promotes a 'we are good-they are bad' chauvinism. We're well practiced at taking sides and we do it casually.
It's part of why I find being supportive a really tricky business, here are two ways things go awry.
The most obvious hypothetical first... It's easy to read a post and slip into a role of empathizing with a person complaining about something.
For example: "Oh, my mother was __________ and she made our lives miserable. ________ are just awful to be around, get that person out of your life!"
That may sound sort of like it endorses another persons suffering and it seems to set up a communication that speaks to shared experience and possibly empathy. But on the other side, if abandonment is a huge fear of people who are plagued with ______, it is going to be dreadfully painful to hear comments that disparage persons with problems similar to _______ as a class. And hearing advice that urges the action that hammers on exquisite fears for them will terrorize them. I can see how that is a bad outcome of what was meant as support.
With respect to the perspective of others, sometimes the others are in the mainstream of group thought. It's easy to slip into the flow of a thread that's endorsing mainstream ideas of the group. For example, someone uses trigger words or suggests a practice such as arm-chair diagnosis that has a group gestalt and the replies go off topic dealing with that side issue (which is simultaneously a group main issue) becoming increasingly distant from an underlying real concern of a poster. I can see how that is a bad outcome of what was meant as support.
I'm not innocent, I do these things, too. I've done at least one of them here. I think they are mistakes, and I make them. That's why I say I struggle with the task of being supportive. I do.