Because we should always take the cop's word for it, right?
Seems to me like he was trying to bait Gates to get him out of the house so he could collar him for DC. Inviting an angry citizen to a public space for "further questions" is clearly a set-up to escalate the confrontation in the view of a crowd. I did not know that Gates had called the chief and complained, now it adds the dimension to it that the officer was probably trying to save his own ass by having the crowd witness Gate's behavior.
1.) Gates's complaints to the cheif would be neutralized by the DC charge.
2.) Officer gets to humiliate Gates for questioning his authority (put that uppity elitist in his place, etc)
After seeing Gates ID, he should have left or at least backed off for a minute to de-escalate the situation
PERIOD. There were other officers on the scene to answer Gate's questions.