TROP alert.
Sadly, the reason this occurs ins't just because of the usual UN malfesance and corruption. Nope, look at the composition of most UN peacekeeper contingents these days; they're from the third world. Let's face it, most of these armies act this way in their OWN countries, why would they act any diffenrent anywhere else.
Notice something different in Iraq? Simple, it's the fact that we're in charge and we're keeping dicipline, and that most of the troops are from the first world or former communist bloc (where they're more liable to try and make a buck off the supply truck or sell Levis off the back of a Humvee than anything else).