The Kassam’s are the product of the fact that the (illegal) occupation is still in full force – either directly (West Bank) or via remote control (Gaza). Contrary to what you think, Israel never ended the occupation. Imagine for a second that an entity occupied all of Israel - One day that entity decides that it will remove itself from Haifa. Yet as it does this, it continues to strengthen its hold on the rest of country (facts on the ground!). Would you call that an end to the occupation? Would you not expect the citizens of Haifa to fight for those in Tel-Aviv, Jerusalem, and Hadera? So I think that you are wrong to assume that what happened in Gaza is proof that land for peace is a bankrupt formula. For Palestinians, Gaza and the West Bank are one entity (Palestine). And as the article above makes clear, if Israel does not leave Palestine, then Palestine will not leave Israel.