It's not that easy to analyze the benefits of military action that prevents some disaster down the road. We are spending a lot of money on homeland defense, but few people bother to balance that against the costs of terrorism.

The WTC attack cost New York City ALONE almost $100 billion.

That's just the cost to New York City.

I can't even imagine (nor can I find hard numbers) what this act cost the United States as a whole in economic disruption, lost jobs, and other fallout. That the WTC attack contributed to our economic problems in the past year or two is undeniable. Certainly many hundreds of billions of dollars.

Anything that reduces the odds of terrorists repeating this act has to be measured against such numbers. I think even many of the people who are opposed to our actions in Iraq would agree that our actions in Afghanistan fall into this category, and certainly homeland defense and other anti-terror measures do.

Now, addressing your point more directly (Iraq, not Afghanistan) and speaking ONLY from a financial standpoint (which IMO is not the most important factor), costs in Iraq need to be balanced against future stability in the region, the economic benefit of a free and prosperous Iraq, lower and stable oil prices, less oppression in neighbor countries, and the other benefits that have been realized in the past when aggressive tyrannies have been replaced by free societies.

An unrelated aside: Two buildings were knocked down in Manhattan. $100 billion. Those who are skeptical about missile defense costs should weigh them against a single atomic warhead in the center of any major city.