Short loving answer.
yes.
Long loving answer.
Well due to the destabilization caused by a poor global market third world countries are only going deeper into the stuff because they have no major source of income. So they decide to harbor terrorists or god knows what in their country as well as smuggle and ship illegal goods through their country, Eg. crack, marijuana, illegal firearms Etc. Some countries, such as the poorer ones in the middle east, due to their naturally perfect climate, soil and such, are even growing marijuana. of course that is the least of our problems cause these massive destabilizations cause civil unrest and wars amongst private militaries, mercenaries, and other various groups, for example, the Rebel tribes in Sudan, the remaining Vietcong, and even the more elusive groups such as the underground communist revolutions of the western world. The fighting groups will cause even more problems for all of the obvious reasons, death, famine, economic strain; but the fact of the matter is that these problems lead to prostitution and that leads to a population boom which can't be handled as well as a spread of STD's such as AIDS. Then again what exactly is a "failed nation" well if you look at my 3 point chart or the 3 P's: Population, Prosperity, and Peace, you can see that many "successful nations" have at least 2 of the points filled; although I admit in these times most countries are involved in a war or an economic crCIA but they all have a controlled population. Failed nations such as Darfur, Congo, or even Ecuador have a poor economy or are involved in some sort of civil unrest or may even have a population that is spiraling out of control. All these ideas lead back to the original point of whether or not failed nations are more of a threat than more stabilized ones and my answer is yes. But of course some developed countries such as China, Egypt, or even Saudi Arabia pose a threat to us economically; such as the case with us maintain a dependence on Chinese manufacturing or a problem militarily such as with Certain countries in the middle east obtaining the materials needed for weapons of mass destruction. Of course though undeveloped countries can obtain these materials as well through more illegal means or even purchasing them straight from the terrorists. So we really should be on the lookout for all countries that may pose a threat to us, in essence, you can never be too paranoid when it comes to multi national negotiations.
Might be missing a semi colon in there somewhere :/