The left has four political goals: 1) To reverse the public perception that they are a bunch of sissy-pants (not Sassypants, which is altogether different).
2) To de-emphasize terrorism as a media issue, because terror concerns play well for conservatives. (See Goal 1 and the sissy-pants problem.)
3) To sell the public, politically, on a hateful policy of treating terrorists nicely, because, like, Dostoyevsky said something like "you can judge a nation by the way it treats psychotic murder-cultists intent on killing as many innocent civilians as possible for no other reason except to masturbate in human blood."
4) To actually reduce terrorism, because doing so achieves Goal 1 and Goal 2, and also would be a great selling point for Goal 3. (See?! It makes no sense but it works!)
Before getting any further, let us note the incandescently obvious that Goals 1-3 are Major Goals and Goal 4 is a sort of "Nice but Not Necessary" sort of thing. If they can accomplish Goals 1-3, in terms of politics, they're all set. If they can sell the public on the idea that a little bit of mass-murder never killed anyone (except for the people it actually killed, of course), they can pretty ignore Goal 4.
Goal 4 is an entirely secondary proposition which merely assists in Goals 1-3. If you nail Goals 1-3, you really don't need Goal 4. And you can pretty much tell they know that by their emphasis on the first three, and blowing off altogether the fourth. ("The system worked," you've no doubt heard.)
Now, on to the slightly less obvious stuff. Slightly.
To achieve Goals 1-3, they have settled on a basic, stupid, unserious, unpersuasive, jackass political message: Only little pussy-fairies are afraid of terrorists and terrorism; real tough strong he-men types, like us on the left, laugh at it as a big joke. Don't you want to join the super-tough guys who laugh in the face of mass-murder? (As long as it's mass-murder killing other people, of course.) So join us, and laugh at terror, be one of the Real Tough Guys with the Cocks of Burnished Blued Steel, and just put your silly-ass concerns about terrorism away. Let's focus on what really matters -- universal health care and the fundamental restructuring of the economy into something more socialistic -- and let us not be distracted by the childish antics of some Muslim head-cases who are, after all, just "acting up" in a particularly aggressive fashion.