The last time I looked, the normal meaning of the term “humanitarian intervention” is a military campaign waged by an outside power or coalition of powers to protect a civilian population from organized violence. The defenseless Bosnian Muslims who were being butchered in the 1990s by agents of Serbia until outsiders intervened were “civilians” in the operative sense.
When people take up arms, not just to defend themselves from state-sanctioned violence, but to overthrow the state victimizing them, however, they cease to "civilians." And, strictly speaking, the help they get in that enterprise from outside powers ceases to be “humanitarian intervention” within the normal meaning of the term. That’s not to say that it might not be advisable for outsiders to help in part because of its benign humanitarian consequences. Sometimes offense is the best defense for a victimized population. But such an intervention stands in need of a different, and much more complicated, justification than humanitarian intervention properly so-called. Sweeping talk about the “responsibility to protect” won't do the job by itself.
It’s perfectly obvious that NATO’s current efforts in Libya can’t be justified in purely humanitarian terms. Consider this CNN report:
When are we going to start hearing an adequate justification for the NATO mission in Libya? We certainly didn't hear it from the president Monday night.