You missed the point. Doctors in the US take 4 years of generally medically-unrelated undergraduate schooling before they're allowed into medical school. Why not just allow them into medical school?
Actually the author forgets to mention that you can have any major to get in to medical school but many medical schools still require quite a few core courses you are expected to complete while in undergrad including two years of Chemistry, a year of math, physics and writing.
In the article, he explicitly compares American doctors with Irish doctors. They both go to school, but the Americans go for about three additional years. There is apparently no real difference in medical outcomes.