Incognito's dad may be a racist- I don't know, and Incognito probably is a giant a-hole but I'm still waiting to hear some evidence to excuse running off on your team.
And frankly, I'm not sure there is any evidence that will excuse quitting. Even if we presume some racial taunting... Well Jackie Robinson didn't quit, and neither did a whole lot of other players who had it far worse. And Martin could have simply gone to one of the coaches, there are certainly more options nowadays then ever before.
You have to deal with adversity in life, and you have to deal with it like an adult.