I found at least some of Michael Eisen's responses to Andrew Kern's tweets. Worth reading (click on the tweets below)-
— Michⓐel Eisen (@mbeisen) March 15, 2016
It's worth looking at PLoS's Core Principles. I'm not seeing anything there they've violated by acting like... a business. And before you leap on Principle 6, "fair price" is generally interpreted as "what the market will bear". PLoS doesn't seem to be hurting for submissions.