A mercenary on the battlefield is looking for a reason not to fight. The only thing he gains is his price and in the old days their share of any plunder. A citizen on the other hand is defending his home, family and country. They are fighting for things which are intrinsic to who they are. Once they are on the battlefield, they will fight.
Every time you hire, you are setting a standard either high or low. The applicant pool will know your employer reputation. The really good quality candidates will steer far from a company who will hire anyone. The good employees know they are good and know what it is like to work with bad employees. They don’t want to waste their time.