Did the US promote regime change in Tunisia or Egypt? The UN authorized intervention in Libya to protect civilians. (The UN has done this many times in the past, which many do not seem to realize.) As a member of the UN, the US participated in that intervention. Without UN authorization the US would have done nothing. Bush (and many other republicans) would have intervened in Libya without waiting for the UN.
In Syria, the UN has not authorized any intervention and the US has not intervened. Bush (and many current republican politicians) would have intervened there regardless of what the UN authorized, but Obama has not.
As liberals most of us believe that representative government with free and fair elections and the consent of the governed is a reasonable goal for everyone even those who do not have it now. Most of us recognize that, while repressive governments exist - always have and probably always will - there are less of them than there were a few decades ago. While we may not be able to do anything about those that do still exist but we should not accept them as 'normal' nor be surprised if people who live in them find occasions to rebel against them.
Liberals espouse a wide array of views depending on their understanding of these principles, but generally they support ideas such as free and fair elections, civil rights, freedom of the press, freedom of religion ...
http://en.wikipedia.org/wiki/Liberalism#Americas
The concepts of social democracy, social liberalism, or democratic socialism all support a commitment to consent of the governed that exceeds the 'right' of dictators to keep their jobs. None of these political philosophies pose that we, as Americans or Canadians or Germans (Westerners in general) have a right to choose who governs us, but the rest of the people in the world have no such right. That does not mean that a country has a right to intervene when people in another country rebel against repressive rule, but it does mean that we should not support the dictator in such situations.