Security Theatre
Despite all the "security theatre" measures put into place, allegedly for "security", or "anti-terrorism" reasons, in first-world countries, I, and probably most of you, can easily think of ways around these measures.
I presume that mid-eastern terrorist group leaders (vs the frothing footsoldiers) are at least as intelligent and creative as Joe Q. Firstworld Public, and could, if they desired to, conceive and execute a plan which would cause major death, suffering, terror, economic loss, etc. in a first world city.
As yet, they have not. Why not?
It's because most of both mid-eastern terrorist group leaders, and first-world political leaders, are putting on performances for their own followers, and it's an implicit, mutual back-scratching mechanism.
The (made-up name) Red Sword Faction sends "The Underwear Bomber", who is quickly caught before he can do his dastardly deed. The first-world politicos point to the Underwear Bomber, and shout, "See?! See?! There is a terrorist threat! Give me/the government more money and power. I'll/we'll save you!" The Red Sword Faction leader points to the Underwear Bomber and shouts, "Behold! Our noble brother struck a mighty blow against the corrupt, un-Godly Unbelievers! Give me your strength (read as: "money") and I shall lead us to victory in our righteous jihad to cleanse the world of (additional pejorative descriptors)!"
Yeah, for the most part, it's about money and power.
There are a few terrorists who come out of left field - think Timothy McVeigh - but not even the most repressive nanny nation/police state will be able to correctly anticipate or stop them (but they'll claim they can). That McVeigh and his ilk can do so much damage is simply a consequence of the power available to inhabitants of this modern technical age.