Second, even if militarily we could, politically it isn't going to happen. Americans are not finished with the War on Terror, but I think they need a period of consolidation---to see that the sacrifice in Iraq was worth it, and this will come as some of the troops come home and there is no civil war, or as the Afghan and Iraqi governments continue to build.
Right now, I don't think ANYONE could "sell" a new offensive against either Syria or Iran to the general public. You can complain about it all you want, but it's reality. Probably, it will take another attack before we take the next step and clean out two or three more cesspools.
It would be great if we were wise enough to see the handwriting on the wall (and what happened on 911 was the essences of that hadnwriting written in large script) and mobilize and defeat those who wish us ill...but in all likelihood, you are right, it will take another, potentially worse attack, to move us there.
In the mean time, the geo-political situation with China and Russia courting Iran, with North Korea supplying Iran with long range missiles (too mauch of this is far too close to:
scenario for my liking), with China courting Venezuela and Cuba (and about every other nation who will listen in our own hemisphere), with China planning to drill for oil 45 miles off our coasts, etc., etc. continues to line up against us.