From a reader:

Just catching up now. I was struck by the fact that Kevin Mattson doesn’t argue with your implication that Upton Sinclair is a liberal saint. Also, he can’t dispute that Sinclair’s book was written to help Sacco and Vanzetti. Instead he meekly complains that the book was “grayer” than you “made it seem”.
So, let’s recap. Upton Sinclair wrote a book to defend murderers he knew to be murderers, but wrote it in ambiguous terms so that he couldn’t be accused of actually defending murderers. Sounds exactly like what the left does. What’s Mattson’s beef?