Supreme Court Justice Samuel Chase took a very active role in politics and was accused of allowing his political leanings to affect his court decisions. Consequently, he faced impeachment (he was acquitted). Here are a couple things you should consider as you form your opinion on this issue.
Most people would probably agree judges should not take an active role in politics. As the adage goes, justice is supposed to be blind, meaning that it should not be influenced by personal bias or political leanings. If a judge is politically active it will cause him or her to not appear unbiased. Without the appearance of objectivity, citizens' faith in the legal system will decline.
However, you could argue that it is impossible to be free of bias and that judges are influenced by their political views, whether they take an active role in politics or not. If judges are politically active, you will at least know their personal biases and can perhaps better judge whether or not they are acting with bias.