The best argument against the War on Terrorism is that terrorism simply isn't enough of a threat to be worth the resources we're pouring into it. On the balance, in a universe that permits things like nuclear weapons, I'm not quite willing to bet the farm on that argument, but I certainly think it's well within the field of factually-viable opinions on the issue.
Bolstering the "terrorists really can't be large-scale threats" theory is this article from the Wall Street Journal OpinionJournal, Iran's Economic Crisis, which I will quote selectively and extensively from:
While social issues continue to poison life in the Islamic Republic, it is economic issues that spell the most trouble for Mr. Ahmadinejad's struggling presidency....
Last week tens of thousands of angry workers, forming an illegal umbrella organization, flexed their muscles against President Ahmadinejad on International Labor Day in Tehran and a dozen provincial capitals. Marching through the capital's streets, the workers carried a coffin draped in black with the legend "Workers' Rights" inscribed on it. They shouted "No to slave labor! Yes, to freedom and dignity!"
...all official statistics show that, with inflation running around 18% and unemployment jumping to more than 30%, the average Iranian is worse off than three years ago. Under the previous administration of President Mohammad Khatami, the Islamic Republic scored average annual economic growth rates of around 4%.... Under President Ahmadinejad, however, the growth rate has dropped to around 3%...
Because it controls the oil revenue, which comes in U.S. dollars, the Islamic state has a vested interest in a weak national currency.... Mr. Ahmadinejad has tried to exploit that opportunity by printing an unprecedented quantity of rials. Economists in Tehran speak of "the torrent of worthless rials"... The result has been massive flights of capital....
The president's favorite catchword is "khodkafa'I" or "self sufficiency." ... "Whatever we can produce we should do ourselves," the president likes to say. "Even if what we produce is not as good, and more costly."... Khodkafa'i has had catastrophic results on many sectors of the Iranian industry.... [food, factory parts and raw materials, textiles, small businesses, oil refining, and gas refining, paper and newsprint, automobile, and copper mining [industries] are on strike].
President Ahmadinejad, however, is determined to impose what looks like a North Korean model on the Iranian economy.... President Ahmadinejad believes that Western-style trade unions and employers' associations have no place in a proper Islamic society where the state, representing the will of Allah, can keep the "community of the faithful" free of class struggle, a typical affliction of "Infidel" societies.
And even this summary has cut out quite a lot of what's there. I read this and I can't help but think, I'm supposed to be frightened of this society? It's feels like worrying Cuba is suddenly going to form a navy and invade Florida, an idea so economically laughable that nobody even thinks about it.
People who feel terrorism isn't enough of a threat to be worth this many resources have good reason to be as upset at the media as the people who still basically support the war's goals (if not the management). The media for various reasons tends to blow every terrorist success out of proportion. Terrorist failures end up either not reported, or de facto suppressed in comparison to their overblown successes. While I do personally think there is a systematic agenda of trying to convince the public that the War on Terrorism is some sort of large-scale failure, you don't really need that hypothesis to explain the current news, simple sensationalist journalism gets you there.
And while the news media has been fairly successful at painting everything that the US is doing as unrelenting failure (rightly or wrongly), and undercutting a significant amount of support that way, it has the effect of creating a narrative of the unstoppable terrorist menace, with truly bottomless manpower and economic resources.
The result is there is still a lot of people who don't see "surrendering" to the "unstoppable" terrorist menace as an option, since if they are indeed that unstoppable, the only thing that even stands a chance of stopping them is killing them before they can terrorize their way to victory. I think this basic line of reasoning underlies the remaining support for the war on terror. (Ultimately, including mine, though I like to think that my own threat estimate doesn't come from this media narrative, but from other sources unspecified in this post.)
But the facts in this article do not point to the genesis of a fearsome society with the resources and desire to take us out. This is the story of a society burning their seed corn and everything they have in a mostly-futile effort to take us out, while we fend them off with ever smaller proportions of our wealth. (By this measure, Iran et al have a far worse disparity to deal with than the Soviet Union ever did; for all the political fretting about the supposed costs of the war in Iraq, the fact is that it has almost no effect on our budgetary priorities whatsoever. Look at the WWII era on that graph for comparison.)
Armies don't go to war, nations, and by extension their economies, do. Asymmetrical warfare may have a good bang-for-the-buck, but it's not omnipotent; eventually the wealth disparity becomes so great that the little guy simply can't compete. (Like the aforementioned example of Cuba, which probably can't afford asymmetrical warfare even in theory since they don't sit on oil deposits.) Terrorists still need funding, which comes from national economies, like those of Iran. If this is the caliber of enemy-funding economy that we are facing, the only real problem is the sheer amount of angry and disaffected people being generated, because there's almost no other way that countries resulting from these policies can afford to bother us. (See also: Venezuela, same song, different key.) Further, those countries where the terrorists win will also enact these seed-corn-consuming policies, eventually making those countries useless, so it's ultimately an unsustainable pathology.
Note this post is just a slice of my full opinion; my actual beliefs should seem unsupported in this post, because this post is about an alternate argument I find out-weighed by other concerns, but interesting and worth talking about. I don't think "just wait for the fire to burn out" is quite the optimal path, just as the fire metaphor would imply, but that can be a viable part of a more sophisticated strategy.