I completely agree with you. If they are willing to publicly trash a former employer and colleagues, what would stop them from trashing me as a new employer? I would be hesitant to hire someone who did this.

They are entitled to write whatever they want, but not taking into account the feelings of the people they were presumably working close with in posting something like this shows a startling lack of empathy.

I'm sure this developer is a genius, but I would take empathy over brilliance every time.

Edit: To be clear, if there is anything unethical or toxic about the workplace culture, they should absolutely post about it publicly to help fix it if that's the best route to address it. This post did not read that way to me. But that's just my opinion.