That's merely an option, not the only option, or the only valid option, or even necessarily the most valid option.

Do the right thing and make someone else be guilty of actively firing me for doing the right thing, (and leave the door open for the theoretical possibility that they don't), rather than me being guilty of giving up, is a perfectly valid stance, even if it's not what you would do.

It's one thing to say "well obviously Matt will just do the obvious thing we all "just know" he will" and it's quite another for Matt to actually do it. One is conjecture, the other is recorded fact history. Matt can no longer say he wouldn't do something like fire an entire board for the crime of doing their jobs. It's valuable to force the issue.

It's a valid stance for a random individual, but not for a board member, who assumes additional obligations that are external to their own personal morals. If your morality and your board duties conflict, your obligation is to resign.