I agree with your comments, and I can see the other side as well (keep ones mouth shut because opening it likely hurts the individual the most), it just seems like the arguments are used so situationally, and I don't understand why. Maybe it is in our nature to be inconsistent?
I think it's a similar vein to speaking about your salary in an open way towards your coworkers. Logically, I don't see much wrong with that behavior but it still makes me feel uneasy. Similarly, I can't really say that I have many reasons against speaking against a company post-firing. If my manager held a large meeting so that my firing was a spectacle, then I would create a blog post detailing my experiences because that would be a very cruel way to let someone go.
I didn't feel like the author was whiny or overly nitpicky but something about the article made me uneasy. It could be because I have the wisdom of the aforementioned phrase "don't burn bridges" in the back of my mind. The author is now less hireable because he made his opinion public. A blog post isn't a Glassdoor comment; a future employer knows that they're hiring a liability that may 'squeal' at a perceived, and possibly valid, slight against him.
Once you get ejected from the cool kids' table enough times for random reasons, you see how not worth it is to put up with their bad behaviour. In the case of TFA, sometimes it's someone else that burns the bridge and there isn't anything you can do. I doubt this post is going to make him any less hireable, he was just in the wrong place at the wrong time.
However, employers should be uneasy about things like this, and not just because of him. Employees have these things called "opinions" and they will happily voice them if given a platform. If we want to continue having a culture where we can hire inexperienced executives and just let them do whatever, we have to be ready to accept the risks associated with it.
It helps other developers decide if they want to work there.
Things like Glassdoor are extremely helpful to employees, in telling them what places are good, and bad, to work for.