When an organization, that you have a leadership position in, does something that you believe is wrong, and you have failed at preventing it and correcting it, then resignation is an entirely appropriate option. Walsh has integrity.
Using twitter to bitch at large about your former employer is integrity? Thats a new one.
"FSF board members are not compensated for their board service, and are not permitted to receive any personal financial benefit from FSF funds or other assets."
https://www.fsf.org/about/the-role-of-the-fsfs-board-of-dire...
It is completely reasonable for a member of a board of directors (or advisors or trustees) of a non-profit to resign if they think the non-profit is going in the wrong direction.