Stephen Walt is a bit less hyperbolic, but he agrees that terrorism simply isn't the kind of danger that could merit the level of response America devotes to it. Unless terrorists get nuclear weapons, he says, they really can't do much damage in America:
Conventional terrorism—even of the sort suffered on 9/11—is not a serious threat to the U.S. economy, the American way of life, or even the personal security of the overwhelming majority of Americans, because al Qaeda and its cousins are neither powerful nor skillful enough to do as much damage as they might like. 
He adds that "post-9/11 terrorist plots have been mostly lame and inept, and Americans are at far greater risk from car accidents, bathtub mishaps, and a host of other undramatic dangers than they are from 'jihadi terrorism.'" He uses the Boston bombing in April as a case in point, describing it as tragic but less lethal than the factory explosion that took place that same week down in Texas. 
Mr Yglesias and Mr Walt are right: conventional terrorism poses no major threat to America or to its citizens. But that's not really what it aims to do. Terrorism is basically a political communications strategy. The chief threat it poses is not to the lives of American citizens but to the direction of American policy and the electoral prospects of American politicians. A major strike in America by a jihadist terrorist group in 2012 would have done little damage to America, but it could have posed a serious problem for Barack Obama's re-election campaign. For the president the war on terror is what the Vietnam War was to Lyndon Johnson: a vast, tragic distraction in which he must be seen to be winning, lest the domestic agenda he really cares about (health-care, financial reform, climate-change mitigation, immigration reform, gun control, inequality) be derailed. It's no surprise that he has given the surveillance state whatever it says it needs to prevent a major terrorist attack.
In a perfect world, as Mr Walt argues, we in the public wouldn't let terrorist strikes dictate our politics. But we're not likely to get calmer about terrorism, because too many people are trying to keep us frantic. At least three parties stand to gain from exaggerating, rather than minimising, our reactions to terrorist strikes. The first is the media, which wins viewership by whipping up anxiety over terrorist strikes. The second is politicians seeking partisan advantage, since panic over foreign-backed terrorism tends to increase voter turnout. (In Israel terrorism shifts voter support to the right. In America throughout the early 2000s, anxiety over terrorism increased support for president George W. Bush, but by 2008 an attack would have increased support for Mr Obama. Similarly, Spanish voters punished the conservative government for the Madrid train bombings in 2004because 80% of the public had opposed the government's participation in the invasion of Iraq. Either way, when terrorists attack, one party or the other is going to make political hay out of it.)
Finally, the third party trying to exacerbate our responses to terrorist attacks are the terrorists themselves, who have generally proven quite effective at choosing targets that provoke widespread media coverage. As hard as we may try to restrain our national responses to terrorism, there will be some pretty smart terrorists out there figuring out how to do things that get our attention again. Even the rather inept Tsarnaev brothers, who only managed to kill three people, did an excellent job of picking a target that dominated the news cycle. Had that attack occurred in mid-2012, it would have completely derailed the presidential campaign. Democrats would no doubt have tried fruitlessly to tamp down public reaction, while Republicans would have allied with the media in hyping it relentlessly.
Politicians do not want to have to deal with these sorts of surprises. They have very strong incentives to go along with intelligence organisations that say they need ever-more-powerful surveillance programmes to see what the terrorists are up to. For Mr Obama, this is a no-win situation. The only thing worse than missing a terrorist attack because an NSA surveillance programme had been blocked would be having the NSA leak that the terrorist attack was missed because you blocked their surveillance programme. Now, having given the NSA what it said it needed to prevent any nasty surprises, he finds himself dealing with a different nasty surprise: the leak of the NSA programmes themselves. And that surprise has made the chances of accomplishing anything on the issues Mr Obama really cares about—health care, climate change, immigration reform, inequality—more remote than ever.