The word "nigger" (notably different than "nigga") is used to basically say to someone "how people used to think about black people was right". It is saying to them that they are less than human, they don't deserve to have rights, they are inferior just because of the color of their skin.
I think that is a lot worse than "person who sucks penises".
That's an interesting and excellent way to put it. I was going to comment that the history behind the N word makes it different than most of those other words (though fa%^ot would be close) but how you put it works well. I have to agree that when people use the N-word disparagingly they are specifically harking back to one of the darkest times in our nation's history and acting like it was all ok.