Here's a post on tumblr to explain it more.
Lilacs & Zinnias • howtobeterrell: x Awards
The whole point is, white people gave them that name and now white people think they can take it away by saying it's "not nice."
That's what defines their struggle as black people and they have the right to say it. That's why.
You have never had that struggle, you do not get to say the same thing.
Ever.
What a non-black person thinks of the word DOES NOT MATTER.