I would say this feature is certainly appropriate for the comments one posts, referring to comments, like on uploaded photos or videos for the purpose of corrections of typos and such as apposed to cut, paste and correct, then add new and delete the older, it should be like every other edit feature on that page - but here, the replies are all based on the specific discussion, generally a question. In that, if there are many replies and you edit or especially add to the original question without it showing as a new reply and the existing replies extend beyond the first page, I think you would never come to a conclusion because by default when the topic is clicked on, it loads the latest replies, therefore you would just post any new information in a new reply and the conversation can continue correctly from there.. Make sense?
My thoughts for the EDIT function were for the possibility of using it before any other comments were made, so the reader can see as polished an argument as possible.
Of course once people have already commented, things are a bit different, yet I would still like the ability to EDIT the original, but this time maybe the print should be in a different color or font.
Well no one is preventing you from replying to your own post or deleting the original.
It would be odd to come into a conversation that starts one way, another person has already replied, then the original poster has changed the first post drastically thereby confusing everyone attempting to read the discussion.