In a free country, the rule of law is intended to protect us from the whims of government. To do this, we require that any law to be written and passed by a legislature, then signed by the executive, both of which are accountable through elections. Judges are then supposed to abide by these democratically-created laws. Obama proposes instead that judges should be able to make decision's based on the judge's political whims ("empathy") instead of the law as written. That should frighten everyone who supports democracy.
For somebody who taught Constitutional law for years, Barack Obama has an awfully odd conception of the judicial role. Orin Kerr collects some quotes from Obama about judges, including this gem:
We need somebody who’s got the heart, the empathy, to recognize what it’s like to be a young teenage mom. The empathy to understand what it’s like to be poor, or African-American, or gay, or disabled, or old. And that’s the criteria by which I’m going to be selecting my judges.
As does Orin, I realize that this is a widely shared view of the judicial role among left-liberals, but that simply illustrates how far left-liberalism has strayed from the rule of law. Settling upon a preferred outcome, without resort to the law, because it favors one group or another ought to be foreign to the judicial role. Judges are supposed to be neutral arbitrators, not having a thumb on the scale in favor of one side or the other. The rule of law means that every one is equal before the law, whether rich or poor, white or black. As the first Justice Harlan wrote: “Our Constitution is color-blind, and neither knows nor tolerates classes among citizens.” That ought to be the criteria by which one picks judges.
UPDATE: Another bit of Sen. Obama's constitional law theory gets dissected here.