A Lutheran pastor famous for his resistance to the Nazis, he has a very famous saying, part of which is:

First they came for the Communists, and I did not speak out—because I was not a Communist," and concludes, "Then they came for me—and there was no one left to speak for me.

In essence, what I am getting at is, the Left do not think the opposite side will come for them. Right now, Antifa is physically violent to innocent people, and Trump supporters. Because the people on the Left tacitly (as they cannot explicitly say so), approve of this, they don't ever think things will turn.

Everybody has to speak out against stuff like this, otherwise, when it happens to you, as a Leftist (as an example), no-one will speak out for you.