When someone says "racist", what they mean is:
There is a systematic, entrenched, system which treats white people as advantaged and privileged and people who are not white as inferior and disadvantaged. This means that although some progress has been made toward equalization of all races, we are still far from true equal footing for all people of all races. What is needed to help with this equalization is for you to realize that the privilege and advantage is still there, whether you mean to benefit from it or not. What is needed to help with this equalization is for you to realize that PoC need safe spaces. What is needed to help with this equalization is for you to help push for PoC history to be in schools. For the teachers to stop writing PoC students off as "going to amount to nothing". For the authorities to stop treating PoC as ten times more dangerous and criminal than white people when we're not.
What some white people hear "racist" what they hear is:
You are a bad person. You are an evil person. You are a Klan member wannabe, even if you don't wear the white hood. You burn crosses on lawns. You use the N word even though you know black people don't like it. You would be like the ones who make the news, dragging PoC behind their vehicles, shooting them for looking "suspicious" and beating them up for fun if you thought you could get away with it. You would back up returning to slavery and segregation! You hate all people who are not white!
Why non-PoC want to be able to say the N word:
They think it's just a mean, unkind, rude, unpleasant word. That's all. Nothing more. Sticks and stones. No different than honky or cracker.
Why the N word offends many PoC:
It is not just a rude word like "dummy" or "stupid" or "asshole". It is a word that was used, for the duration of slavery and beyond, to keep PoC oppressed, and to remind them that if they stood up for themselves they would be whipped, beaten, attacked, mutilated, and KILLED. Let me repeat: KILLED. We fought hard for the right to be treated like HUMAN BEINGS. The N word is an indication that there are still many white people out there who don't think of us as HUMAN BEINGS and don't want us to be treated like HUMAN BEINGS. So it's not just "black people are being mean and not letting us say it." Cracker, by the way, does not mean little thing with salt on it that you put cheese on. It means the one who cracked the whip while PoC were slaves.
So think about these things before you start getting defensive at PoC. And think about why you're getting defensive. Think about why you want to deny the truth of other people's experiences when you have no way of having that experience yourself.
Why do you want to be able to say a word that is sending the message to PoC that you want them to be as they were during slavery and segregation times. If you don't want to send that message. If you don't sincerely feel that way, then there is no valid reason -- NONE -- to want to use the word.