There are numerous reasons why Elena Kagan should not be confirmed by the Senate. Here is one:
She is the Solicitor General for the Obama administration. The Solicitor General represents the President in matters before the Supreme Court. That means she advocates on behalf of Obama and tries to persuade the Supreme Court to rule in Obama's favor. From Obama's point of view, how could you do better than appointing someone to the Court who already has a history of advocating on your behalf? Are we really supposed to believe that she will be impartial and make the transition from advocate to neutral judge? This is not a Kagan- specific criticism; every Solicitor General should barred from being appointed to the Court by the same President that named them Solicitor General. It would be like Phil Jackson going from coaching the Lakers to NBA ref. With no job or time in between. Would the NBA let him ref Laker games? Of course not. His time as a Laker coach would create a conflict; people would not perceive him as being neutral. The same goes for Kagan, how can we think she would be neutral on the Supreme Court when she was just advocating on behalf of Obama before that very court?