I understand all the factual information you pointed out, I just disagree that black people getting to say "nigger" while white people can't is racist, or important for anything other than historical reasons.
The point I was trying to make is, when you're dealing with a racial slur, the most important thing is the intent of the speaker. I don't think a black person *is* universally OK with being called a "nigger" by another black person. I think if they are friends, or if they share cultural markers that suggest the word isn't being used in a hateful way, it's more likely to be OK. There are, however, black people who are brutally racist toward young black men, and when they say "nigger," I'd bet it comes off the same as if an old white guy had said it.
I don't think "gay" parallels "nigger" at all; it's more like "black," where it can sting in the right context, but it's a generally descriptive word. I'd say "faggot" is the word you're looking for. While it's true that the specific orientation of the speaker doesn't matter a lot, in my experience, gay people are a lot less tolerant of angrily being called "faggot" by an older, conservative religious person than they are of gay allies playfully calling them "faggots." Because perceived intent matters.
I'm not saying this is the way things should be (frankly, I'd be happy for slurs like this to never be spoken again, except in history books), but this is generally the way things are. I certainly understand being frustrated that what appears to be the same behavior is unacceptable for white people, but often OK for black people. What I'm saying is, it's different. The legacy of slavery and segregation and racism in the US is such that the word "nigger" carries different meaning when spoken by a random white person than when spoken by a random black person. The word is designed to carry the weight of centuries of oppression, and it carries it whether you want to or not, regardless of the fact that you aren't racist and haven't done anything to perpetuate that system.
So why do you want to say "nigger?"