A news source aiming to independently investigate and report where reality stands in relation to opposing political talking points is an opportunity for bias, but you're guaranteed bias against reality if you don't do that part, is the thing.

Most folks haven't thought about that too much, though, and/or haven't had much education in politics and media, so "fair and balanced" and "we report, you decide" resonate as slogans, rather than smelling fishy.