My best friend is 'highly sensitive' and found the literature around 'highly sensitive person' very helpful. Hope you find it, as suggested upthread, incase its helpful for you, too.
As for other people's opinion, I dunno if it would help you, but I really can't imagine getting upset about something an entirely unknown person posts on a message board, even if it is in response to something i have posted. I think people's posts mostly tell you more about them, and their response, than they do about the original topic. That's just the way it is.
Very different to a comment from someone who knows you, but, even then, it usually says more about them than about you.
Sometime, of course, these responses can be helpful, because we see that we are not the only person struggling in that way or because it shines a light on something of which we had not previously been aware.
It may be that feeling this way, is one of the many consolations of getting older. Hope you can find a way to insulate yourself a bit more from unwelcome comments. HTH.