It is most certainly a legitimate point of debate. I believe Israel is vital for our security for two reasons:
1. The more philosophical approach that I outlined earlier whereby our ultimate security, that is, what it is we need to defend, is our freedom. To the extent that enemies of freedom gain strength and friends of freedom become weak, it is to our detriment.
2. In this specific case, I view the arab world similar to that of the soviets. I believe they are an expansionist, and evil empire. This battle is not about the way some borders are drawn in Israel. This is about freedom, and the Islamists desire to conquer the world and enslave all non-islamist males.
If your interest in purely one of short-term self interest for the U.S., then at least look at it this way: Israel is the first line of trenches. When they are overrun, the battle will take place at the second line, and ultimately the third. We already know that they have their eyes set on Spain, and some would say that they already have their eyes set on the U.S.
With respect to the war America faces, you touch on a critical point here. They are expansionist. They are evil. Thus far their "empire" is perceived as borderless, though I'd wrap a number of states up within it. Borders are meaningless. We are, at this stage, at war with an ideology. We need to recognize that now, and defeat them. Not when the "borders" of our enemy have been "politically" defined at a far greater cost.