The idea that American taxpayers ought to pay for free medical care for anyone who manages to cross our border is mind-bogglingly stupid, guaranteed to drive away the swing voters Democrats need to win the presidency. Yet it received unanimous support last night at the second Democratic presidential debate.  Given the poor state of health of poor people from third-world countries, their per person yearly health care costs would be higher than for the average American, and we can't afford to provide taxpayer-funded health care for all of our own without busting the budget. Moreover, the offer would act as...