Controlling for income, Caplan explained, well-informed poor people favor very different policies than poor people who are not informed. Informed how? Well, he explained, one could administer tests of general political knowledge -- e.g., How long is a U.S. senator’s term? How many states in the union? Does the U.S. belong to NATO? -- as well as others about specific aspects of economics. Those who pass the test would be given the franchise.
His idea has met resistance, most often, he said, from those who believe this will mean that the interests of the poor will be ignored by politicians. Caplan though points out that voters who passed his test, whether rich or poor, favor similar policies, meaning that in this context class interest is not a valid concept.
Here is where my father's instruction (he was a professor of political science) helps. Bryan thinks that the point of elections is to get good policies, so it makes sense to require people to pass a test before they can vote.
An alternative view comes from Murray Edelman, who wrote The Symbolic Uses of Politics. For Edelman, the goal of much political activity is to obtain "quiescence." In layman's terms, this means that government is obeyed, rather than defied or rebelled against.
If the point of elections is to keep the masses quiet while the elite rule, then restricting the franchise is going to be every destabilising. It would give those who are unhappy no outlet other than armed revolt. In fact, one theory of political economy (I associate it with Acemoglu) says that nations become more democratic and redistributionist in order to fend off revolution.