They are being fired for (a) essentially explicitly stating they are not gonna do a good job working in the way the company thinks its employees should be working (b) trying to get the company to change through “open letters” through the press.

Both (a) and (b) are reasons for firing on their own. It has nothing to do with differing opinions.

It’s like me telling my team that since the Product Owner did not prioritize the feature I think is critical for us to work on first, I will not really do a good job with working on the features the PO did prioritize.

The company would be foolish to fire me because I said our PO sucks and makes terrible decisions. The company would not be foolish to fire me because I said that because I disagree with the PO I’m gonna do a half hearted job. Especially if the way I communicated this to the company is through a half page advert in the NYTimes.