Where had all the civility gone before the rampage in Arizona, this newfound cordiality that 9-year-old Christina Taylor Green never got to see? It's as if we keep our good-heartedness on ice - only to be thawed in case of emergency.
"If this tragedy prompts reflection and debate - as it should - let's make sure it's worthy of those we have lost," President Obama said last week at a memorial service for the six people who were killed and 13 wounded by a gunman.
And sure enough, our hearts poured out anew. In tragedy, we find opportunity to "expand our moral imaginations," as Obama put it, and "sharpen our instincts for empathy."
No heckling or partisan cheering at the State of the Union speech next week; maybe even a nonpartisan seating arrangement. Even the upcoming health-care debate is not likely to be as acrimonious as it was shaping up to be.
A deranged killer might be inclined to think he'd done us a favor.
Too bad Obama could not have attended Saturday's candlelight vigil for Juan Moreno Aguilar - a 25-year-old who was stabbed to death during a random attack in Prince George's County.
The speech in Tucson would have been just as appropriate here, perhaps more so. Moreno was the 10th of 13 people killed by violence this year in a county just outside the nation's capital, Obama's back yard.
"For those who were harmed, those who were killed - they are part of our family, an American family 300 million strong," the president said in Tucson. "We may not have known them personally, but surely we see ourselves in them."
Of course, not every law-abiding American gets treated like family.
Moreno was walking with a friend through the parking lot of a Shoppers Food Warehouse in Langley Park when a group of youngsters apparently mistook him for a gang member. Although his vigil was attended by Rushern L. Baker III (D), the newly elected county executive, only a handful of concerned citizens showed up.
"We want to send a message that we are all in this together," Baker said.
But are we really?
The homicide of a little-known Hispanic man has about as much chance of generating widespread sympathy as, say, the death of a resident of Juarez, Mexico, by people wielding firearms bought in the United States. We just don't see the connection to us, as if they are not part of our human family.
For most of us, the lives of the Morenos of the world aren't worth so much as a blip on our emotional radar. We discount their deaths as easily as we do those of civilians in Afghanistan who get killed by our missiles, fired from drones as easily as we fire off nasty anonymous notes via e-mail.
Little wonder that our current state of goodwill is not expected to last. The love for our fellow man goes only so deep.
If the nation needs reminding about anything, it's that all life is valuable. And that you don't have to be a member of Congress or a federal judge or an extraordinary elementary school girl - and the suspect in the shooting need not have the face of evil personified - to make us care.
"It probably asks too much of human nature to expect any of us to be restrained at all times by persistent modesty and empathy from committing rhetorical excesses that exaggerate our differences and ignore our similarities," Sen. John McCain (R-Ariz.) wrote in The Washington Post on Sunday. "But I do not think it is beyond our ability and virtue to refrain from substituting character assassination for spirited and respectful debate."
McCain had expressed similar sentiments during the 2008 presidential campaign, during which people turning out to see his running mate, Sarah Palin, could be heard yelling crude remarks about Obama.
But his words did not resonate as much back then, and probably would have only if someone had actually done Obama harm.
Why does it take a tragedy?
On "PBS NewsHour" the other evening, New York Times columnist David Brooks told host Jim Lehrer, "I really think there's been a psychological, emotional shift nationwide among Republicans and Democrats, which leaves me and I think a lot of people a little more hopeful that things - you know, that there could be some lasting residue."
And before you know it, the residue we're talking about is a powder burn from another political gunfight.