the decision may or may not be dumb, but appealing to the popularity of a decision is never logically sound. There have been incredibly unethical things done throughout history with far more than 1/3 approval.
I think it's pretty sound in this case. A policy change that causes 1/3 of your company to resign in protest is definitionally dumb (unless you're a believer in the "I meant to do that" school of thought being suggested elsewhere in this thread).