If you (the general "you", not you specifically, and hopefully not you at all :) are working someplace where this sort of anonymous nastygram to a manager is the most pragmatic way to make your voice heard, the fact that you work in that sort of environment is a much bigger problem in your life than whatever problem the anonymous nastygram might help with. Your time would be better spent finding a new place to work rather than sending anonymous nastygrams.
The best possible outcome from an anonymous nastygram still leaves you working someplace where the only way to make your voice heard is via anonymous nastygrams, and that's unacceptable as a long-term solution for anyone, anywhere. As a short-term solution to a specific problem, it's still not likely to help- it'll just foment paranoia and ill-will. In fact, the passive-aggressive approach is probably only going to have a constructive outcome with managers who care enough about their employees that it would be better to just talk to them anyway. The terrible managers this is designed for will just double down on their terribleness if they were to receive something like this.
I don't think anyone's suggesting that someone in this situation should quit their job and then start looking for something new. No one should ever do that if they can reasonably avoid it. But that person should definitely be putting all their energy into finding a new job rather than trying to patch up their current, unfixable employment situation to be more bearable.
The best possible outcome from an anonymous nastygram still leaves you working someplace where the only way to make your voice heard is via anonymous nastygrams, and that's unacceptable as a long-term solution for anyone, anywhere. As a short-term solution to a specific problem, it's still not likely to help- it'll just foment paranoia and ill-will. In fact, the passive-aggressive approach is probably only going to have a constructive outcome with managers who care enough about their employees that it would be better to just talk to them anyway. The terrible managers this is designed for will just double down on their terribleness if they were to receive something like this.
I don't think anyone's suggesting that someone in this situation should quit their job and then start looking for something new. No one should ever do that if they can reasonably avoid it. But that person should definitely be putting all their energy into finding a new job rather than trying to patch up their current, unfixable employment situation to be more bearable.