In this case I think the cop had a good reason to ask for ID. The house had been called in as a possible burglary in progress and Gates approximately fit the description of the suspects. That the cop then refused to show his own ID is inexcusable.
In the given situation I would agree that Gates
could have been more co operative.
He is not obligated however, to be co operative with unreasonable request. He is required to give his name and address. That's it. If the cop is still suspicious, he can go do his cop work and gather some evidence that would give him a reason to believe the man is not who he says he is. Until then he has a reason to think otherwise, it's just a cop taking the easy way out rather than obeying the law and observing the man's rights. Sure, Gates could have appeased the cop, but he was under no obligation to. So, the cop used force in order to find out that there was nothing out of the ordinary going on. .....what's that you say? It required force to figure out that everyhting was OK? that is what betrays the officers conduct.