Far better, I think to own up to any personal opinion and then do a fair reporting job; doing so would tend to disarm criticism on bias grounds. The burden would not be to imply bias (thereby insinuating a story is inherently invalid) but to debate the content of the story on its merits. My beef with what Armao did is that her coverage wasn't balanced, for all that her tilt went against her personal opinion.
The executive editor's position strikes me as somewhat hypocritical: Armao got the axe not for having bias or making inappropriate decisions but for her candor about same. I suspect that plenty of editors are making exactly the same decisions for exactly the same reasons--and abdicating their responsibility just as much--but by not owning up, they remain safe in their jobs. Armao's comments were made in an email, which once sent is inordinately difficult to delete or deny. I suspect that a similar sentiment voiced privately might not have carried such a penalty, and I'm nigh-positive that journalists and editors express opinions to each other all the time without worrying too much about their credibility. So again--was she forced to resign because she was biased, or because she for one admitted it?