[jamespitts]

Board members have a different level of culpability than the management at the firms which they help govern, due to the kinds of decisions they are commissioned to make and the information they have access to. Board members may also find themselves misled by management.

As part of the governance process, Walt Mossberg does bear a certain amount of responsibility for what Facebook management has allowed to happen on their network, and I interpret his action here is part of his taking that responsibility.