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.
Class resentments, as well as race, may effect an officer's response to challenges. An affluent white guy who responds to questioning from a working class cop by referencing his superior social, intellectual, or political credentials doesn't deserve to be treated abusively but should not be surprised if he is. Even middle class white women (like me) may be taught early on not to be rude to cops.
So I remain agnostic about the role of race in Skip Gates's apparently illegal arrest and find discussions about racism the case has sparked to be generally unenlightening. Officer Crowley seems to think that he can disprove the charge of racism by telling us that, years ago, as a Brandeis police officer, he tried hard to revive the late Reggie Lewis when he collapsed on a basketball court. (Some of my best friends are African-American, he might as well have said.) Others have reflexively accused the police of racial profiling, but police did not stop or question Gates initially simply or primarily on account of his race. He was treated abusively perhaps because he was black, or perhaps because he exercised a right, more often honored in theory than in fact, to offend a police officer.