It's wrong to say al-Qaeda "could always kill people" in a bunch of other ways. In fact, the evidence suggests that they can't.
Matt Yglesias says he's skeptical about the value of ratcheting up security even further in airports, and then adds this:
The last point I would make, raised by DanVerg on Twitter, is that even if airplanes were completely secure you could always kill people by detonating a bomb in some other crowded place. For example, you could blow something up in a crowded airport security line.
I'd take something different away from this. The fact that al-Qaeda keeps focusing on airplanes is a sign of how weak they are. Sure, they could detonate a bomb in a security line, but it wouldn't kill very many people and it certainly wouldn't have the psychological impact of taking down a jumbo jet. Alternatively, they could try to blow up a chemical plant or something like that, but that's out of their league. They'd have to get a team of operatives into the country and then they'd have to do all the planning and all the execution within the borders of the United States, where surveillance is far greater than it is in Yemen or Nigeria. They plainly don't have the resources to do this, and every in-country plot we've uncovered since 2001 has been bumbling and amateurish.
Obviously this could change, but at the moment I think it's wrong to say al-Qaeda "could always kill people" in a bunch of other ways. In fact, the evidence suggests that they can't, at least not in any wholesale way. In that sense, then, airport security really does seem like one of the better places to focus our security efforts. I just wish we could do it more sensibly.