No one's going to defend a white teacher by claiming an anti-white slur is a fighting word, so the kid learned a valuable lesson.
Sure because, bear with me here, different races are different.
While we should strive as a society to provide people equal opportunities to excel in America, it's obvious that there are differences between races, and that needs to be recognized as well.
That said, there are pejorative you could throw at a white person that I feel would make me kinda blase about any response. They aren't exclusive to white folks the way the hard "R" is to American black folks, but they are out there. Pedo, Nazi, and Commie, if said to me in earnest, probably earn an ass whooping.
Next I'll blow your m8nds and point out the two sexes are different too.