Forcing a regime change in Iraq allows the US to pressure the remaining fragile, dictatorial Arab governments to install more democratic institutions, without fear of losing the control of the world's oil supply to fundamentalist, anti-western movements.
The safety of the entire world is a concern with the rise of fundamentalist Islamist groups in the wake of the Arab Spring and the possible nuclear ambitions of Iran and North Korea.
The way that Carter left the Shah of Iran to flap in the breeze and eventually to be swept out of Iran by Khomeini and his band of not-so-merry fundamentalist pranksters hardly inspired confidence in the U.S. by the petro-wealthy of the Arab world.