A mural of car attack victim Heather Heyer in Charlottesville. (Steve Helber/Associated Press)

The Aug. 20 Outlook package of essays under the heading “Hate of the union” and a separate essay titled “What the ‘alt-left’ antifa activists actually believe” did a good job of putting the issue in context, but they did not fully articulate the grave damage violence from the left does to the larger progressive movement.

Rogue police forces around the world have long been known to insert paid provocateurs to wreak havoc in order to discredit nonviolent protests. Clearly, there are some antifa groups who are glad to volunteer to do that work for free. This violence captures the media’s attention, drowns out the progressive messages of a protest, drives away people who would join a cause, gives cover to the violent right-wing extremists and allows right-wing politicians such as President Trump to get away with blaming both sides equally.

It is essential that progressives commit to strictly nonviolent principles. We need to denounce and separate ourselves from those who claim to express anti-racist and egalitarian values by smashing store windows, lighting fires and beating up their opponents. Far too much is at stake to allow groups such as this to hijack the progressive movement.

Peter MacDowell, Alexandria

The writer is a retired progressive organizer.