Well, as a practical matter, the USA tends to support despots in the Middle East who support us and our goals (and Mubarak is one of those guys). Meanwhile, we tend to be afraid of democracy in many Middle East countries because we know that if they are allowed to vote freely, the people there are very likely to elect governments who are hostile to the USA (and Israel), or even elect hardline Muslim theocracies.
In the long run, democracy is a good thing, but in the short run, it's going to lead to a lot of countries run by guys like the Muslim Brotherhood. It's not an easy call from the USA point of view.