That is essentially what X did. King offered unity, healing and a better future.
It worked for King, it worked for Ghandi. Do you really think there could have been something like the civil rights laws -- born primarily of white people -- if the primary black person had been X and not King?
Yet it was Ghandi himself who, when asked if his peaceful tactics would have worked against Hitler, said, "probably not."
I'm not suggesting that white people are literally Hitler, but simply that there's a time and place for everything, including peace and violence. And I say that as someone who has never called for violence on anything ever.
A speech calling for violence in the time of newspapers and television is surely more damaging than that same speech given in an auditorium in the early 1800s to a select group..
I am not attempting to put a 'value' on the whole of slave trade, that's impossible. I'd merely like to point out the 'apples vs. oranges' nature of your comparison.