Azoy?

K. So I know what you are thinking but I am not racist but have a serious questions.
How come you hear one black guy saying Nigro or My Nigar one to another yet when white guys saying it it becomes wrong.
Isn't it wrong to say it no matter who's mouth it comes from ?
I would think it's just as bad coming from one black guy to another as it's a word meant to put down a person.
Someone please enlighten me with why it's right for one black person saying it to another and it's not as offensive if at all.
Seriously this thread is not to offend anyone but to educate myself on the issue.