The "Simple" son asks simply why we have the Seder, and this is given a simple, satisfying answer. While the "Wise" son is a role model, the "Simple" son is a moral standard. While some people want to change the world, others don't. It is still important that they ask, and want to know why they should be thankful. Even if we have everything we need, we should still understand, even to a lesser extent why it is that way.