I followed all of your links. In the first two, the word "violence" appears nowhere in the text. There is a photo of a cardboard sign with the slogan "White Silence is violence" but that proves nothing. I can find photos of all kinds of crazy slogans on signs.

The Houston Chronicle story does feature an interview with Cherry Steinwender, executive director of the Center for Healing Racism, explicitly endorsing this point of view. That is the first actual data point I have seen.

The Google Scholar search brings up a lot of articles containing the phrase "silence is violence" but a lot of them are red herrings having nothing to do with the matter at hand.

So that's one valid data point. Better than nothing, but still a long way from a self-evidently mainstream point of view as McWhorter claims.