Have you ever had an argument that was just mediocre? But later you think of a witty retort that would have been just perfect. Thats what rebasing is. Its re-structuring the conversation the way you would have liked it to go.
If you restructured the "I Have a Dream" speech, you'd be hacking up history. If Martin Luther King Jr restructured the speech prior to August 28, 1963, as I am sure he did many times, history remains untarnished.