Fred actually has some very good talking points on this issue. His stats are correct, for one (with the exception of "fifty seven gazillion dollars", but that was good sarcasm, there).
The cost of fighting terrorism Vs. the results are staggeringly unbalanced, to put it mildly, and make no sense at all, if anti-terrorism is the only aspect you view it from. Since this has gone on for a decade, cost a trillion + dollars (including Iraq in the anti terror war), cost hundreds of thousands of lives - mostly civilian "collateral" casualties, anyone looking at it has to honestly conclude that there is a different, underlying motivation for all this blood and money spent. It ain't so much because the US and allies are altruistic holy warriors striving to remove evil fanatics from the world. Nation building is also infrastructure for industry and business building, and the implied co-goal is that the newly built nation will be cooperative and beholden to the builders.
It's about huge potential money from metals, it's about gaining geopolitical and geoeconomic power, it's about access to valuable resources that make the first world nations function and progress.
Afghanistan is a wilderness. Most of the people are barely educated to uneducated, and semi-literate to illiterate. There are virtually no proper roads or highways, virtually no railway lines, limited communications towers, etc. etc. outside of a few small cities.
With such a rugged, mountainous terrain, the country is an extremely expensive blank slate to develop, but the pay-off for that investment of time and effort and money is potentially huge. Eventually, it will happen. Eventually, I fervently hope (with little optimism) that the Afghan people themselves will be truly sovereign and in the loop with the rest of the world. They could enjoy a prosperous and happy existence, if things went as they deserve. It is their country, those are their metals, and they fiercely love and defend it from all comers....as they have since Alexander the Great.