The United States, as an entity, ties a person's value to his or her humanity. We fought a civil war over judgment based on skin color. We endured massive civil unrest to establish a kind of equality for labor, and social protest to extend the franchise to women. We continue to argue over other forms of superficial difference.

We have stopped lynching blacks. We don't blackball Jews and other non-Christians as much as formerly. (We're experiencing a period of Muslimophobia, but we've never been an entirely reasonable people.) We allow women to vote, and even to work and own property. We print public information in more languages than English, which is actually only good customer service. We have slowly made our public facilities more friendly to people with physical impairments.

We can stop making excuses for our bad behavior toward each other any time. All it takes to be an American is a willingness to buy into the American experiment. Let's not pretend that tribal loyalties can't be extended to the whole tribe. Violence doesn't have to be biologically predetermined, any more than monarchy is.