 Since they contract with their employers to defend citizens from violence, then they have created that obligation to their employer.A negative right to life allows an individual to defend his life from others trying to kill him, or obtain voluntary assistance from others to defend his life—but he may not force others to defend him, because he has no natural right to be provided with defense.To force a person to defend one's own negative rights, or the negative rights of a third party, would be to violate that person's negative rights.