Jane Galt eloquently describes  one of the most critical and persistent logical errors made by those who see (or imagine) a problem and immediately call on government to solve it:
Tyler Cowen  points out that Medicare was twenty years behind private industry in covering prescription drugs. Ezra responds 
that that’s just because the insurers and drug companies wanted it that
way. Which brings up one of my perennial peeves about people advocating
national health insurance or any other big programme: they point out
all the ways in which public choice problems make the current system
suck, and then proceed to outline their future plans as if those
problems will somehow magically fall away in their system.