I don't agree that having only bad candidates is "an edge case which only happens in thought experiments". It's easy to get blinded by the all-to-common sports team approach to party politics (My team good! Other team bad!), but issue for issue, there just isn't any appreciable difference in the candidates.
So what is the "key difference" between the parties? Rhetoric. When Republicans advocate a small contraction of the welfare state, Democrats claim that Republicans totally oppose the welfare state. And many Republicans oblige them by standing up for "liberty" and "responsibility." Similarly, when Democrats advocate a small expansion in the welfare state, Republican claim that Democrats oppose free markets. And many Democrats oblige them by saying things like "markets only benefit the rich."
This rhetorical illusion is so powerful that when a Democrat like Clinton adopts many pro-market reforms, Republicans still hate him as a 60s radical. And when Bush II sharply expands the welfare state, Democrats still hate him as a billionaire's lackey.
So what is the "key difference" between the parties? Rhetoric. When Republicans advocate a small contraction of the welfare state, Democrats claim that Republicans totally oppose the welfare state. And many Republicans oblige them by standing up for "liberty" and "responsibility." Similarly, when Democrats advocate a small expansion in the welfare state, Republican claim that Democrats oppose free markets. And many Democrats oblige them by saying things like "markets only benefit the rich."
This rhetorical illusion is so powerful that when a Democrat like Clinton adopts many pro-market reforms, Republicans still hate him as a 60s radical. And when Bush II sharply expands the welfare state, Democrats still hate him as a billionaire's lackey.
http://econlog.econlib.org/archives/2008/09/how_dems_and_re....