I think you should get back what you put in, qualification wise. if you went to med school for 8 years and got paid a construction worker's wages, i can guarantee you'd be pretty pissed off.
It's also what you contribute to society; imo, a doctor contributes more to the economy, so he gets a higher pay. A construction worker's job could be done by a wider range of people, so the wage for that job is not as big as that of a doctor.