A comment by TMLutas on Sometimes, I wish this was a collective blog
Unfortunately, the real threat of the have nots is not in ak-47s, etc. though conventional kinetics can be the basis of pretty outsized strikes (see 9/11). We depend on discovering new antibiotics faster than poor sanitation and genetic micro-evolution breeds resistent bugs. Have not markets are ideal breeding pits for superbugs (think SARS and avian flu). Below a certain yearly income, polities don't care about the mad scientist doing odd and dangerous things out in the middle of nowhere. They just like the income that the mad scientist brings. That's another threat, whether it's bio, techno malware, or nano-threats (grey goo). In fact, there's a whole list of things that require global coverage to prevent real threats to our safety and wellbeing and the notties don't have the resources to do their share. There is no wall we can build to prevent these threats from spreading. All we can do is spread the protective systems we already have in place in the first world throughout the globe. This is why it was a good idea to eradicate smallpox for instance as a matter of self-interest and not just as a matter of charity and solidarity.
Once you get past the ludicrous idea of ak-47 wielding 3rd worlders sacking Washington DC, the nots do really have the potential to hurt us and badly, often by inaction. Just because the threat isn't sexy doesn't mean it is not real.
Al Gore is still a tool though.