On the other hand there are plenty of managers who would love to work in such a system because it provides perfect cover for them when they want to really screw

On the other hand there are plenty of managers who would love to work in such a system because it provides perfect cover for them when they want to really screw with employees, scapegoat others for their own failings, etc. One manager at a previous employer at mine would be particularly interested in this kind of management style; he practiced it well enough on his own. Also, if this internal board is anonymous I'll eat my dirty underwear. I guarantee you the "L2 and L3 executives" (and probably the department heads) can attach names to posts, or have the means to order it done, if they really want to.