You have a constitutional right to talk back to a police officer; and whether Skip Gate's account of his arrest or the police version is closer to the truth, it seems clear that Gate's speech rights were violated and his arrest was illegal. Less clear are the officer's motivations for the arrest. Naturally, the prevailing assumption and apparent, primary source of Gates' outrage is the belief that the officer, James M. Crowley, is a racist; but that ignores the equally plausible possibility that he's simply a bad cop, (or maybe a not-so-bad cop having a very bad day,) who would also have arrested a late middle-aged white guy whom he deemed insufficiently deferential. (If you find this scenario implausible, you never met my father.)
I'm not denying the persistence of racism in the criminal justice system, which is apparent to anyone familiar with the abuses of capital punishment, the drug war, or racial profiling. I am simply pointing out another problem, which may account, at least in part, for Gates's arrest: police officers, and other law enforcement agents, can become quite jealous of their authority, (as even a routine airport encounter with a bad TSA agent may demonstrate.) Wearing a badge and uniform and carrying a gun does not always bring out the best in people.