Interfering in the internal affairs of sovereign countries is illegal under international law.
It has been done at times for humanitarian reasons (by NATO forces in Bosnia in 1995) particularly when genocide was clearly happening.
Humanitarian intervention didn't happen in Rwanda in the early 90's where ethnic cleansing by majority Hutus against the minority Tutsi's was clearly evident. The same for Cambodia where Lon Nol's Khmer Rouge was conducting genocide. These were two clear cases of genocide where the world stood idly by.
So the record of responding to genocide is "spotty". There may even be unspoken racism connected with the "positive" interference for humanitarian reasons (Bosnia) and why it was not done in other instances (Cambodia, Rwanda).
Of course another category of "interfering" and ignoring a country's sovereignty is by pre-emptive invasions and or clandestine operations (by the CIA and hired mercenaries) which are done almost exclusively and with impunity by the U.S. which ignores international law whenever it wants. But this is a whole other issue and not the focus of this short piece.
Regarding the revolutionary uprisings in the Arab world these past months, any interference by outside forces was not only unnecessary but unwanted by the protestors in those countries. These were (are) all grass roots and populist revolts against the country's dictators and their regimes.
That is until now with Libya the country in mind and the megalomaniac Muammar Qaddafi the tyrannical leader.
The uprising in Libya has seen Qaddafi use genocidal methods i.e. the arbitrary shooting and murdering (by hired mercenaries), strafing and bombing (by war planes and helicopter gun ships) of peaceful demonstrators or innocents standing idly by.
In his speech yesterday, Qaddafi was unapologetic, vowing to show no mercy against those he described as "cockroaches". He vowed never to give in and was willing to die to the last ounce of his blood.
At this point the focus is on Tripoli, the capital which he and his security forces hold fortress like. Benghazi, the second city, Tubruq and other cities to the east have been captured and now held by the protestors. But the residents of Tripoli are under siege and where reports indicate much of the arbitrary killing (by mercenaries) has taken place.
Protestors outside of Tripoli have vowed to "liberate" the capital. But the people of Tripoli are living in legitimate fear, almost hostages and victims to Qaddafi's madness.