He was arrested on his own front porch, after the cops IDd him, because he was loud? Why is being loud an arrestable offense? Don't most noise ordinances require an attempt to get a person to voluntarily comply?
Why didn't Crowley simply leave when he knew that Gates had a legitimate, and legal, reason for being in his own home? Why did he call for backup, and thus escalate the situation? Why didn't he simply leave?
The reason is simple, his authority was challenged, and he reacted like any macho prick would in that situation, he hit back with his power to arrest someone for a BS reason. Your defense of him perpetuates the problem, cops are not there to arrest people, they are there to serve and protect the public. The public was not in danger from an old man who needs a cane to walk, something even Crowley recognized, or he would have placed his hands behind him when he cuffed him.