I keep coming back to one tweet. Amid a steady stream of rage driven by pain and sorrow, a note of grace. Twitter stalwart and all-round decent bloke Lew Stoddard wrote:
"The mosque on Clyde Street is besieged by flowers and candles. A steady stream of people from all walks of life arrived during the 15 or so minutes I was there, including local scarfies dressed up for St Patrick's day, with gifts, food, or just to pay respects.
"And their humility and depth of aroha is magisterial. 'We failed him,' they told me. 'He lived with us in this city & we let him turn out this way.' And they expressed sorrow for the decades he will spend in solitary confinement.
"The Clyde Street mosque was his original target."
But it wasn't the only such note. We also heard Farid Ahmed forgive his wife's killer, saying he would pray for him. "I think probably he went through some trauma in his life, probably he wasn't loved … I don't hate him at all, not at all."
And it might be the only way out of this.
A year ago, Mother Jones reported on the American "Life After Hate" movement seeking to reform white supremacists: skinhead members of real and violent gangs. It is a terrible and difficult problem. Those who could not find pride in the content of their character found it instead in the colour of their skin.
When race becomes identity, stopping racism is a lot harder than, as is sometimes suggested on Twitter, finding Nazis to punch. At least according to the activists working to de-radicalise white supremacists, confrontation hardens attitudes rather than changes minds.
One of them said: "The uncomfortable truth is that the best way to reform racist thugs may be to offer them precisely what they aren't willing to offer others, and precisely what many people in this polarised political moment feel they least deserve: empathy."
It is hard counsel when every instinct screams for retribution. It is even harder counsel when we reflect on the injustice. It is blindingly obvious that we would be seeing far less compassion if a Muslim migrant had killed 50 white New Zealanders in a church. Every racist would, in that world, be emboldened.
But the logic of aroha is sound in either case. When attacked for being a member of a group it is far more natural to defend the group than to denounce it — especially when much of one's self-identity is bound up in group membership. It only hardens positions.
An invitation to talk with others who had doubts about their own membership in racist communities, and to then join with other "formers" as a new identity, can simply be more effective.
The statements of incredible grace from Friday's survivors should make us all want to be better people. If any members of Parliament regret having found electoral advantage in race-baiting and xenophobia, their own path to aroha may inspire others who badly need to make that journey.
• Dr Eric Crampton is chief economist at The New Zealand Initiative.