The idiocy of our country’s approach to medical marijuana was on full display for all to see at the Minnesota Vikings training camp yesterday. Since the age of 10, Percy Harvin, a Vikings wide receiver, has suffered from chronic, debilitating migraines. Luckily, later in life, Harvin found a therapeutic substance that not only relieved his migraines effectively, but also allowed him to play football. It was marijuana. But during last year’s NFL combine, Harvin, a promising prospect, tested positive…