The temptation here is to deploy Emerson's quote about foolish consistency, but I have to admit that I tend to see ethnic ties (from my first book) and xenophobia (from my second book) everywhere and perhaps more than they are relevant.
Others, especially Jon Western, have done a great job of arguing that there was something there to stop--that is, there was a real risk of a mass killing to prevent. I would only add to that one of the pieces of social science that is relevant: we know that overwhelming victory tends to end civil wars more durably but also more bloodily. That is, when one side wins outright, they tend to engage in large scale killings of their opponents. So, if we abstract away from the particular case, we can still expect that Qadaffi would killed lots of folks had the outsiders not stepped in to prevent the fall of Benghazi.
Of course, the title of the piece, pretense, suggests that there is an ulterior motive. While we can speculate about Sarkozy's interests in terms of domestic political strategies (wag the chien),* for the US and UK, the domestic gains are less obvious. If one wants to say anything about oil, the reality is that the old strategy has always been the best one for cheap oil--support the autocrat. Indeed, one of the problems in the Marxist-type arguments about resources and intervention is that outsiders usually can get resources from the regime or its opponents, so it is often not so obvious that supporting the rebels is the best way to get the resources. Given that US relations were at the best with Qaddafi before this wave of dissent and repression, it is hard to say that Obama needed to support the rebels due to a thirst for Libya's oil. The Europeans could be more concerned about access to Q's oil, but again it is not clear why supporting the rebels would be the way to go.
* See Roger Cohen's piece that puts France and Germany into perspective.And this is here I only partially embrace my own foolish consistency. I do think that some of the motivation here is immigration prevention--xenophobia. But I recognize that the interventions of many are motivated and/or justified by the real concern about watching dissidents get killed. What Kuperman fails to highlight is that Qaddafi's opponents did not start by fighting but with protesting. They fought back after getting shot at. No small distinction there. Again, I am contradicting my own earlier work by suggesting something was contagious here. The decisions to support the Libyan rebels are linked to the positions taken by Obama and others with regard to Tunisia and Egypt (and even Bahrain, sort of).