I have a post about this on the L.A. Times LiveCurrent blog, but I reproduce it below. The question posed was, "Is it appropriate to ask a Supreme Court nominee his/her views on specific issues that are likely to come before the court?" Here's my response:
Tough question -- good arguments on both sides. Right now, let me just air one.
Judges are obligated to think carefully about the parties' arguments in every case, and be open to changing any preconceived views they may have. Naturally, they'll often adhere to their earlier views -- but sometimes they do reconsider. (For some examples of how justices' views have changed from one decision to another, see here; but they may also change their minds from their pre-confirmation views, when they first face a concrete case that requires them to seriously focus on the matter.)
Occasionally, a justice's vote will deeply disappoint those who wanted to see him on the Supreme Court. It might even differ from views he stated in pre-appointment opinions or articles. But observers will generally just assume he changed his mind, though they might bemoan the change.
But imagine a justice testifies under oath before the Senate about his views on (say) abortion, and later reaches a contrary decision. "Perjury!" partisans on the relevant side will likely cry: They'll assume the statement made with an eye towards confirmation was a lie, rather than that the justice has genuinely changed his mind. Even if no calls for impeachment follow, the rancor and contempt towards the justice would be much greater than if he had simply disappointed his backers' expectations.
Faced with that danger, a justice may well feel pressured into deciding the way that he testified, and rejecting attempts at persuasion. Yet that would be a violation of the judge's duty to sincerely consider the parties' arguments.
Of course, there'd be little pressure of this sort in a political system in which people assume their adversaries are basically honest, disagreements represent honest differences, and changed positions represent honest changes of mind. When you find such a political system, please let me know.