The Left and Right Are Living in Different Realities

The way Washington's spending grows, in libertarian mythos, goes like this: Republicans want to spend money on X but not Y, and Democrats want to spend money on Y but not X, so they reach a grand, bipartisan compromise to spend money on both X and Y, in ascending quantities, forever. It's simplistic, as myths are wont to be, but it tells some truth.

Recently, I've been thinking about how divergent Americans' risk assessments appear to be—how we seem to have increasingly different ideas of what endangers us and our...