John Lewis was the youngest speaker at the 1963 March on Washington—where MLK gave the "I have a dream" speech—and the speech Lewis wrote that day was so incendiary that the march organizers wouldn't let him deliver it as written.
On the day before the march, the Catholic archbishop of Washington DC, who was scheduled to give the opening invocation, received a copy of John Lewis’ speech. He freaked out.
Arguments over Lewis' speech continued during the march itself—even while speakers were addressing the crowd from the Lincoln Memorial, Lewis was huddled in a guard station inside, by the Abraham Lincoln statue, with Dr. King, A. Philip Randolph, and others, negotiating changes.
Lewis was 23 at the time, by the way. King was 34. A. Phillip Randolph was 73.
In the end, the group negotiated more than a dozen significant changes to the speech, each of which moderated its tone and substance and many of which have particular resonance today. The final typed version was completed just moments before Lewis took the stage.
So what did they change? I'm glad you asked.
The first problem came in the speech's second sentence, where Lewis said the movement couldn't fully support JFK's civil rights bill, because it was "too little, too late." That got changed to "we support it with great reservation."
Why didn't Lewis support the civil rights act "wholeheartedly"? Well, this line, appearing immediately after the one above, gives an indication: "There’s not one thing in the bill that will protect our people from police brutality." That line was struck entirely.
And right after that, a line referring to the bill's failure to "protect young children and old women from police dogs and fire hoses" had the words "in the South" added to it.
(On several occasions, including right around here, references were added to the bill "in its present form"—not entirely unreasonably. The bill wasn't finished, and it was seen as more productive to push for improvements rather than reject it as inadequate.)
Next, Lewis had written that the Kennedy civil rights bill ("in its present form" in the final version) would not "protect the citizens of Danville, Virginia, who must live in constant fear in of a police state."