Why DC series motor should be started with load?

In any DC motor, the speed of the motor is inversely propotional to the flux and directly proportional to Back EMF . 



When starting a series motor the current flowing will be high, but the flux that the motor produces will be moderate since the series winding has less number of turns. 



Hence, if u start the motor without load the speed will increase. 



As speed increases the back emf