What do you think would happen if the US and all of Europe completely pulled out of the Middle East? Would Israel stay the size it is now? If not, can you really say it's "purely defensive"?
Also, "pulling out" is too simplistic. There are not only troops on the ground, but also military bases, joint exercises, weapon sales, commercial ties, industrial ties, scientific collaborations, cultural influences, and so on and so forth. Short of disappearing from the globe the US cannot just 'pull out'