I'm gonna take issue with the word "bias". I think it's quite overused and devoid of some meaning. To me, bias is when you discount facts to follow a predetermined conclusion. Bias is when you absolutely will not, under any circumstances, believe that a certain source or position could be correct, no matter the evidence to show that it is. Tending to trust one side or source over the other is perfectly natural. More credible sources ought to be trusted, and positions that advocate better stances ought to be supported. Do I generally assume that something Bill O'Reilley says is probably nonsense and that something Jon Stewart says is probably true and insightful? Yes. This is because most of what Bill O'Reilley says is nonsense and most of what Jon Stewart says is true and insightful. If Bill O'Reilley said something true and insightful and Jon Stewart spouted nonsense, would I listen to Bill and not Jon in those circumstances? Yes. That is what I think makes me not biased.
I think in order to qualify as bias, actual ignoring of reality is necessary. Refusal to open one's mind beyond a predetermined position is bias. Prejudice is bias. Determining and judging with a trend is not. So sayeth Pasch.