Deliberation and Ignorance
First, the public is not as ignorant as Teson thinks. Certainly the public has not mastered the social theories of the experts. But the public knows lots of things that the experts do not -- things about how policies and conditions materially impact them and interact with other aspects of their lives (the classic example is Brian Wynne's research on how post-Chernobyl British government policy hurt sheep farmers because it failed to account for how sheep farming is actually done). The public and the experts have complementary blind spots.
Second, the ignorance level of the public (and of the experts) is not fixed. Teson's argument may carry some weight with respect to holding referenda on policy issues. But that is clearly not what proponents of deliberation are proposing -- indeed, they are fierce critics of that kind of preference-aggregation model. Deliberation involves an intensive process of evidence examination and debate, set up in such a way as to give the deliberators responsibility for crafting policy. Effective deliberation is what happens in institutions like Community Advisory Groups and citizens' juries. Time after time, social scientists have documented laypeople's ability to master complex topics and make critical use of experts' input. In a world controlled by technocrats, it may be rational to be ignorant. But when one enters into a deliberative process, it becomes rational to understand the issues in detail -- and so people do.
Deliberation is not a panacea, and it's difficult to do it well. But I had hoped we had moved beyond objecting to it on the basis of public ignorance.