If PA is pushing authors for expressing dissatisfaction, perhaps said writers need to hire lawyers.
You shouldn't live in fear of expressing your cpinions on the internet. Also, if you have to go out of the way to hide your true identity, then you lose all credibility because anyone can make any claim under a false identity.
Also, if PA is that bad, why not let them find out what you think of them? Wouldn't you be wanting the association to dissolve?