White blood cells are good. Except if there are too many of them. And especially if they decide certain parts of your body doesn’t belong, things can get nasty rather quickly. Perhaps a crude picture of what’s going on in Syria right now – but crude is all there is time for here.
The immediate question is less about why, who and how many, as it is about the astonishing inability to have it stopped. Essentially: Why could international support and agreement be reached over Libya – including support from the Arab League – and no such thing seem even remotely possible for Syria? Why do things grind to halt at the sanctions level (a level that has proven – repeatedly – to be as effective as taking aspirin against AIDS.)