*all I'm saying is why is it a word (or any word) that some people can say and others can't
*
Because it's a word that was used by one group of people against another with devastating consequences. It's a word that did more than just make a particular sound coming out of a mouth - it demonstrated pure hatred & a belief that one group of people were less human than the other. It was the word used when one group of people elected not to sit next to the other group on a bus, or drink from the same water fountains, go to the same schools or use the same toilets.
It's a word that has the effect of hurting one group of people far, far more than they could ever hurt the other group in the same way...so the very fact of it highlights inequality.
Think on that. Assuming you're white (as I am) how would you genuinely feel to be called "white trash"? Miffed? Indignant? A bit cross? I personally wouldn't feel any more than that & would probably dismiss it as a stupid insult. That's because there is not one single word that could be directed at a white person as loaded with history & hatred as the N word is. Racism can, of course, be directed at anyone, but the personal wounds it can cause are significantly greater for some people than for others - for very obvious reasons.
So, just don't use it. By actively refusing to use that word, hopefully you are performing a courtesy that takes no skin off your nose but indicates your acknowledgement of racism & willingness to be part of eradicating it. That's why you shouldn't use it, never mind why anyone else does.
Black people who use it towards each other are using it because of it's historical implications, not in spite of them. You can't get rid of a word - if it exists, then it exists. But you can change the meaning, or at least the context in which it's used. You can use it ironically and by doing so alter the effect without losing the historical significance.
To just take the view that it's only a word and anyone can use it you'll simply be legitimately putting it back in the mouths of the group of people who used it so horrifically in the past. And why would anyone want to do that?