The other day, a Muslim saved a terrorist.

It happened just after midnight Monday in London. The terrorist, according to authorities, was Darren Osborne, 47, from Cardiff, Wales, who drove a rented van 150 miles to the British capital, where he jumped a sidewalk and plowed into a crowd of worshipers outside a mosque as people were attending to a man who had collapsed.

Osborne is reported to have screamed, “I want to kill all Muslims!” The outraged crowd dragged him from the van, punching and kicking him. They might have killed him, but then Imam Mohammed Mahmoud of the Muslim Welfare House put himself between the mob and the man. “No one touch him!” he ordered. “No one!”

Mahmoud later told reporters it wasn’t just him, but “a group of brothers” who were “calm and collected and managed to calm people down.” As a result, Osborne was still in one piece when police arrived.

At least 10 people were reported injured in the attack. The man who collapsed later died, though the cause is unclear.

Mahmoud’s moral heroism seems especially stark in light of what Osborne allegedly did. Not just the random maiming of innocent people, but the fact that he did it, one presumes, in protest of terrorism.

That’s more than simply mad. It is also visceral proof of the human tendency to become what we abhor. The German philosopher Friedrich Nietzsche put it like this: “He who fights with monsters should look to it that he himself does not become a monster. And if you gaze long into an abyss, the abyss also gazes into you.”

That would seem to be what happened to Osborne. It seems to be happening to many of us, the dangerous absurdities and frightening expediencies of this political moment having a coarsening effect on supporters of otherwise honorable causes.

So that a man who opposes the devastating agenda of the Republican Party devastates a GOP baseball practice with rifle fire. And people angry about police randomly killing African Americans randomly kill police officers. And people who protest the destructive words of conservative firebrands commit destructive acts to the tune of $100,000 damage in Berkeley, Calif. Now Darren Osborne apparently decides to protest terrorism by committing it.

We become what we abhor. We become the monster we fight. Small wonder. Few things are more attractive than violence cloaked in righteousness. This is especially true in a morally disjointed era wherein politics is broken and down is up and up is sideways and violence, like the snake in the Garden, whispers temptations and seductions. People who never would have listened before find themselves listening now.

That’s why Mahmoud’s example is powerful. His ability to separate himself from the anger of those people in that moment is a reminder that no one is predestined to be swept away by righteous anger into unrighteous acts. Being moral is a choice, albeit sometimes, a very difficult one.

Some will surmise that Mahmoud was able to make that choice because he’s a faith leader. But that’s a convenient rationalization that removes from the rest of us the onus for doing the right thing even when the wrong thing is alluring and nobody would blame you for it.

It is probably closer to the mark to believe he did it not simply because he is an imam, but because he is an upright man who realizes you can’t take the low road to the high place. And that Nietzsche was right: when you gaze into the abyss, the abyss gazes into you. You cannot control that.

But you can control what it sees when it does.