I don't even use the word but...
The term "nigger" originally meant criminal, lowlife, etc. Over time it became a term used solely when describing Africans.
The term "nigga" started as a way for African-Americans to turn a term of hatred into a term of endearment. The word "nigger" would never, ever go away, so why not take the hatred out of the term?
Regardless of all of that, the word is simply a word. As Bryden said, it only has the power and meaning that you give it. I can call my girlfriend or any female friend a bitch, and 100% of the time they are not offended. Why? Because both sides recognize that there is no ill-will behind my use of the word. Same logic, I'm a white dude with dreadlocks. I am very used to hearing myself called "dread, dreadlock, Rasta, etc." I'm never offended because it's typically not offensive, to be simple. But when I was arrested and the skinhead cop kept calling "dreadlocks", I took offense to that. He knew my name, he had my ID. He was referring to me as "dreadlocks" in a way that conveyed a negative feeling toward me.
Honestly it sounds cliche, but there truly is a HUGE difference between niggER and niggA, I don't care who says otherwise.