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Editing posts would cause chaos... People would post ridiculous things, wait for people to get their jimmies rustled, then change what they said. It would take trolling to a new level, causing many people to become fed up with the forums.
Wouldn't editing posts cause some amount of integrity loss in the forums? NSG doesn't necessarily count here...
I know many don't know/use this, but there is a preview button, so, in theory, shouldn't ever post be "correct" and not need editing?
Are we talking editing every individual post you've ever made or just being able to edit thread opriginal posts?
If posts are editable there definitely needs to be a way to see the original post.
But as for link not displaying right or picture doesn't show up, etc., that is what the preview button is for. That's the point I made above, instead of making a sale thread or something and trying to race to get it done, the preview button beautifully shows how your post will look, pictures, links, etc. and changes/corrections can be made before the mistake occurs.
It does make sense if you forget something, but I think if you start with a short time frame, it will be slowly expanded over time.