What will ruin his plan is that even if you considered it the most rational thing on earth for a country to pay for protection, the political sell to the domestic populace is practically impossible to make. Even when nationalism is not at the top of the agenda like now, its a permanent undercurrent in every country's politics. You don't survive long by prostrating to other powers, even when they are stronger than you. I've seen countries move against their own interests (in my opinion) for nationalistic reasons on much milder issues than this idea of ever straight up paying for protection.