What is the plan exactly when fighter jets escort a passenger aircraft to a landing?

Obviously I mean when a terrorist threat has been suggested. These situations are occurring quite often now in the wake of 9/11 and I'm curious to know what exactly can be achieved by scrambling a couple of fighters to intercept. Of course it's better than doing nothing but how much better?
There seems to be only two possible courses of action:
1) Force the aircraft to land. I don't think a terrorist intent on killing is going to obey whether he is control or merely compelling one of the crew to fly.
2) Shoot the hijacked aircraft rather than permit it to crash into a highly populated area. Who in this country have we got that would have the balls to order that? Hundreds of innocent civilian passengers on the plane would certainly die plus an untold number on the ground. It would be an enormous catastrophe and I just cannot imagine the scale of the repercussions. The country would be bogged down for decades with endless public and government inquiries, legal wranglings and so on ad nauseum until the very crack of doom.
I really don't see the point in doing something merely for it's own sake when nothing at all can be gained from it. But I'd just like to see inside the head of the person who thought of it in the first place. TELL ME THE PLAN MAN.