Simple fact is: Crowley was the one who choose to waste his time for treated Gates as an intruder/suspect in first place. Yes what he did was overreaction. I think that Crowley was the one most responsible for this incident getting out of hand.
Looks like it's time for a game of "Put Yourself in Their Shoes".
Now, suppose you're a police officer driving around Cambridge, Massachusetts. You get a call about a break-in in progress. You say to your partner "Nah, it's a waste of time."
Dereliction of duty- you're fired!
And that is why you are not a cop. But suppose you have a good partner who says, "You have to respond or else you'll get fired" and you say "Oh, right. Thank you". You drive to the house. Now remember, the information you have is that there are intruders inside the house. You don't know if they're armed or dangerous. The owners may be in trouble inside. You walk up, see a man inside, say to your partner "Meh, he's probably the owner. Don't want to waste his time" and start to walk away.
Dereliction of duty- you're fired!
And that is why you are not a cop. But suppose your partner says "We can't assume he's the owner until we verify. There may be people in trouble in there. We don't know the situation yet," so you say "Oh, right. Thank you." You walk up to the door and ask the man to come speak to you because you're investigating a report of a break-in. He flies into a rage and starts accusing you of racism. You say to your partner, "He's probably the owner. He looks pretty mad. Why else would he say that? We should be respectful and leave."
Dereliction of duty- you're fired!
And that is why you are not a cop. But suppose your partner says, "Well of course an intruder's going to claim to live there. You have to actually verify that he's the owner and nobody's in trouble," so you say "Oh, right. Thank you." You ask him if anybody else is inside and he yells that it's none of your business while accusing you of being a racist cop. He walks away and you say to your partner "Well, I can't go in there. I don't have a search warrant."
Dereliction of duty- you're fired!
And that is why you are not a cop. But suppose your partner says, "The Supreme Court has said you don't need a search warrant if you're investigating an intrusion," so you say "Oh, right. Thank you." You walk in and, he asks for your name and you give it to him (see the police report:
Henry Louis Gates, Jr. Police Report - July 23, 2009) but he keeps yelling over you. You tell him you need to see his ID and he finally shows you his Harvard ID. You say to your partner, "OK, he lives here. I'm going to call in my findings and leave"...
Good work, Officer Liebling.
You try to call in but you can't hear because the guy is yelling so loud, so you head out towards the porch. The guy follows you out. So now you're outside the house with this guy yelling and ranting at you. Neighbors are gathered around and you say to your partner "Oh no, what do I do?" He says, "Well, you could give him a warning and then arrest him for disorderly conduct if he keeps it up." You say "Oh, but that violates his first amendment free speech rights." Your partner says, "Actually it's not. You're not arresting him for what he's saying, but for his behavior. Disorderly conduct is not protected by the Constitution." You say, "You may be right, but I'm just going to let it be"...
OK, that's fine.
But still remember, you are not a cop. If you had years of experience under your belt, you might find it more prudent to arrest him.