Why does the U.S. support dictators and then tell the entire world that we support democracy?

We have backed Egypt's President for years. We backed Saddam before turning on him. We backed the Shah of Iran before having him overthrown. We backed numerous Pakistani dictators. We backed the Mujhahideen (which later became the Taliban and then Al-Qaeda) to fight off the Soviets. The right wing contends that the middle easterners have irrational hatred towards the west. They also don't understand why people in Afghanistan and Iraq are trying to fight off the West. However, don't you think people in the middle east have a legitimate reason to not trust us given our track record with them? Furthermore, isn't it hypocritical of us to now tell the Egyptians that we support democracy, even though we have supported their dictator for years?