Here’s one peek into Matt Cassel’s character: On Jan. 26, he and his wife saw smoke and flames billowing from their neighbor’s house in Loch Lloyd, Mo. Cassel, the Kansas City Chiefs’ quarterback, ran to the house, pounded on the door and rang the doorbell repeatedly. That got the attention of the woman inside, who didn’t know she was in danger. The house was heavily damaged, but the woman escaped unharmed.

The woman, the firefighters and a witness said Cassel was a hero, and that the story might have had a tragic end without his actions. Cassel’s response: “The real heroes are the firefighters.”

None of this was on the minds of thousands of Chiefs fans Sunday. They were more concerned with Cassel’s two interceptions and two fumbles in the team’s game against the Baltimore Ravens. So when Cassel was thrown to the ground and knocked out of the game with what would prove to be a concussion, a significant number of Chiefs fans cheered. They actually cheered their own quarterback suffering a serious head injury.

A handful of fans have loudly defended their actions in the days since. They argue that Cassel signed a $62.7 million contract, they paid good money for their tickets and they have the right to do what they please.

But most, no longer shrouded by the anonymity afforded from being one in a crowd of 70,000, have gone silent, and that is an ironically boisterous commentary about the state of public discussion in the United States in 2012.

It’s easy to cross the line of basic civility when you’re yelling from afar, with like-minded voices, secure in being part of a faceless crowd and not even sure that your target really hears you.

The Internet, like a stadium, allows a person to rant, attack, profane and conceal any sense of humanity, knowing his identity is almost completely protected. It debases the country’s tradition of having a spirited but civil debate as part of our continual evolution into a better place.

We all have the right to complain, whether it’s about overpaid and underperforming athletes or similar public officials. Heck, we even know an editorial cartoonist who poked fun at Cam Newton’s Superman dance. But to cheer when someone has been hit with what could be a season- or career-threatening injury goes way too far.

Fans seem to have forgotten it’s only a game, whether it’s those Chiefs fans, or Atlanta Braves fans throwing debris on to the field after a bad call or soccer hooligans sparking riots. In all those cases, anonymity is a precondition, lack of accountability an accelerant.

These days, it’s even bleeding into email, Facebook and other encounters where one’s identity is known.

Whether we’re talking about Matt Cassel or Barack Obama or Mitt Romney, the question is not whether you have the “right” to cross the line from expressing your opinion to lacking basic decency. It’s whether that’s who we really want to be.