The answer you get from people who seriously want to give them the aide for FA reasons are:
Israel has historically relied upon Western (chiefly US) military assistance to maintain a significant stockpile and sophistication of arms and military preparedness to dissuade military action against it from its neighbors and other actors who are openly hostile its existence as a state;
Israel’s prosecution of its current conflict has significantly depleted those stockpiles of armaments to the point that they no longer constitute such a quantum as to provide adequate deterrence to an attack.