I think the reason people (including me) hate this particular idiom is that it adds nothing. The quote itself is sufficient emphasis without the sentence fragment "This." attached below it. Oftentimes we see a comment reply consisting solely of the word "This.", again, adding nothing that the voting system doesn't already do a better job of.

And now I have added nothing to the actual topic, which was a somewhat irrelevant to HN but amazing discussion of life in Cairo this week. Sorry.