Some excerpts :
A decade ago an independent international commission that elaborated on the idea of "responsibility to protect" spelled out six criteria for deciding whether military action is justified. Essentially a modernised version of centuries-old Catholic standards for "just war", these criteria are: right authority, just cause, right intention, last resort, proportional means, and reasonable prospects. Bitter experience, from Kosovo to Afghanistan, has taught us that "reasonable prospects" (ie of success) may be the most difficult to judge and achieve.
Applying these criteria, I remain unconvinced that a no-fly zone over Libya is justified – at the time of writing. If it turns out that Gaddafi does still have a secret stock of chemical weapons, and can drop them from the sky, this judgment could change overnight. We should prepare contingency plans. But we have not yet exhausted all other avenues, including trying to pry Gaddafi's cronies away from him by fair means and foul. A no-fly zone would be very difficult to enforce, and might not have anything more than a marginal impact on the ground.
Above all, any form of armed intervention by the west – and the US military says a no-fly zone would require initial bombing of Libyan radar and anti-aircraft facilities – would spoil the greatest pristine glory of these events, which is that they are all about brave men and women liberating themselves.