Why is anyone struggling with this?
The N word has one meaning when coming out of a white person's mouth - one. It's never had an alternative meaning & has always, in every circumstance, been used to dismiss, demean, insult and attempt to diminish black people.
So basic manners, if nothing else, ought to be enough for all of those who give a shit about such things to simply not say the word. It's not a hardship...no one NEEDS to say it, so just don't.
So, why can black people say it? Because they are saying it to each other, and they don't have a history of using the word in the same vicious way, with all the associated civil rights abuses, that white people do.
Context matters...and if you can't see that the context of a white person saying it & a black person saying it are very, very different, then there's something the matter with you.
And, in many circumstances, the word is already banned...depending on context, of course. Try using it to refer to a black person at work or in public and you'll see just how banned it is when you're arrested &/or sacked.