Some people report events objectively despite their bias, and some don't. Katie Couric obviously isn't hiding hers since everyone here recognizes it, so what's the problem?
Katie is pretending to be a newswoman, which implies fairness and objectivity. That she is readily recognized as being biased demonstrates a fundamental dishonesty.
Opinion column writers, partisan hacks, and advocates like Lanny Davis, Ann Coulter, Maureen Dowd, Charles Krauthammer, Sarah Brady, Wayne LaPierre, etc. can be taken to task for outright lies, but one
expects them to support a particular viewpoint, and defend it in a debate; that's fine since full, open, and vigorous debate is generally good for society.
But objectivity - or at least an effort to achieve it - is
expected from a journalist.