Lew Rockwell recalls the ending of universal conscription in the early 1970s. The late Milton Friedman was against the draft, and argued for its elimination. Friedman and Gen. William Westmoreland had a famous back-and-forth, the end result was which Friedman showed the superiority of a “mercenary” army, i.e. volunteers.
Niccolo Machiavelli was against “mercenaries,” but in that sense, he meant foreign sympathists to a certain cause who willingly join a fighting force for its sake. Either way, I think Machaivelli was wrong on this one. Mercenaries/volunteers are better because they already bring a sense of morale and willpower to the mission.