I don't necessarily feel that the incident was racially motivated. What we have here is a man who was probably tired and a little cranky from travelling who returned home to find, to his further annoyance, that his door wouldn't open, and that he needed assistance to get in. Then the police arrived to investigate whether he was a burglar, and he probably didn't show the degree of deference that the cop would have preferred (in his place, I doubt I would have, either). So, the cranky academic took offense to what happened, probably wondering if it was because of his race, maybe feeling embarassed that all this was taking place in view of his neighbours. What I don't understand is why this resulted in an arrest. Cops are trained in conflict management, they know how to deescalate situations. All the officer needed to do was to explain that he was only doing his job, and that if it had been an actual break in, Gates would have been appreciative. And then he should have left the premises, end of story.
While I can certainly imagine Gates being angry, I find it hard to believe that a respected Harvard-employed academic would resort to "yo momma" type insults toward the officer, that just makes no sense whatsoever. I dunno, this whole thing sounds to me like the cop was a bit of a hothead who refused to take Gates' perspective, and did nothing to try to mitigate the situation.