Judges take an oath to apply the laws of the State and the United States in a fair and impartial manner. That makes sense and we applaud the fact that our judges are beyond the reach of political squabbles. However, judges are human. That means that they carry with them their own bias arising from their own upbringing, religious background, and life experiences. We seem to accept the fact that some bias is understandable. In fact, there is no way to accomplish a 100% unbiased decision.
What we are really saying is that we want our judges to be less biased than the rest of us in making a decision. We do not like the thought of judges making arbitrary decisions based upon their own backgrounds. If we start with the premise that judges are incapable of being unbiased then we are able to first establish the foundation for moving in that direction. If we start with the understanding that judges are all biased in some way, shape or form, we then can work to identify the outcomes we want the judge to decide.
For example, in a custody case, a judge carries his/her own bias on family issues. However, if we identify the outcomes we want in a custody case (ie: likelihood of high school graduation, no drug abuse, etc.) then we can take steps to start measuring (scientifically) the components that derive the outcomes we want. If the goal is to ensure high school graduation then we can measure the components that lead to high school graduation. Things like exposure to domestic violence, drug/alcohol abuse, mental health concerns all become relevant and important factors to measure to ensure the outcome we desire. In taking an approach based on measurements of the components instead of the characteristics as a whole, we can lessen the bias that is inevitable when the decision is left to the judge.