You really have to look at the possible outcomes from this uprising. The Egyptians made it clear that Mubarak's time as ruler needs to be over. Mubarak had only 2 realistic responses: Step down (either now or later) or Tienanmen - Egypt style. The later choice would cause him and Egypt more harm than the first choice because he would lose support from the west, US financial aid, and cause more anger against him.
The US had to chose Mubarak or the protesters. If the US sided with Mubarak and not ask him to change power then it would only project more hatred and more animosity against the US not only in Egypt, but throughout the Arab world. It would reduce US credibility as a supporter of freedom and democracy. Even if the US supported Mubarak to stay in power the US would never allow him to pull a Tienanmen. Anything but a Tienanmen or Mubarak's rapid ouster would quell the people. So thus, the only rational choice for the US was to support Mubarak's ouster or transition.
Do we know what will take it's place? No. If we sided with Mubarak and the protesters kick him out would we have more or less influence in the new government that would formed? No. If we side with the protesters will the US at least be able to say we sided with the supporters of freedom and democracy and thus try to play a positive role with the new government or help shape the new government? Yes. That is the best possible outcome we can hope for right now. The administration did the right thing.