The simple reason for the West to remove Gaddafi is not that he's been a thorn to the U.S., but he's highly respected and regarded by other African nation leaders. With him removed, other leaders in Africa could easily fall or be controlled by the leaders of the West. With total disregard and contempt for African nations, the US-led NATO continue to attack Gaddafi's forces despite the Arab League and the African Union condemnation.
The obvious attempt to assassinate Gaddafi violates not only U.S. law, "without authorization from the U.S. Congress pursuant to the terms of the War Powers Resolution, for President Obama to establish any type of so-called "no-fly zone' over Libya would be illegal and unconstitutional", but also the UN's own charter which prohibits state-sponsored assassination, except under conditions of warfare.
No state has declared war against Libya.
As expected, the mainstream media paints Gaddafi as the monster attacking his own people, just like they did to Saddam Hussein in a run-up to the U.S. invasion of Iraq.