In our society, the Supreme Court acts as the body that interprets what the constitution means and establishes legal precedents. It is important that the Supreme Court justices do not fall victim to political pressure because their decision will impact millions of American citizens. If they simply listen to the advice of politicians, then it completely throws off the balance of power established by the US Constitution.
The balance of power incorporated into our political system must remain, otherwise politicians will control what laws are made and will determine what is constitutional/unconstitutional. This would give politicians too much power, to the point where corruption could easily occur.