From a comment at Megan McArdles blog:

The WoT was an existential war, for about two weeks after 9/11. My most shocking post-9/11 moment was hearing a generally anti-war and anti-American German acquaintance rage about how the world needed to band together and nuke Afghanistan into glass, “put an end to these guys once and for all.”

Problem was, when the shock war off, the memories wore off with them, because there wasn’t a series of consecutive events to remind people that this wasn’t an isolated incident, it was merely the first time the self-proclaimed enemy had managed to work out all the details into the butter zone. And would happily do it again, and did…Bali, Madrid, 3/11. (Unsurprisingly, das German was complaining bitterly about the Afghan war as little as three months later.)

So rather than finding a united willingness to work out a measured and effective response to the threats of global terror, even though it would mean difficult and tragic decisions, we get wild and vascillating policy preferences ranging from “stupid and ruinous war set up by lying Bush…” to “invade Iran”.

In WWII, they didn’t have that, especially in Europe. In the offchance the average Londonite was prone to make a “if you think about it, less people have died in incident X than have died in car accidents” argument, the whine of a V2 would quickly refocus the thought processes.