It was not "introduced". It was approved by the Sacred Penitentiary as being without fault that anyone could use with just reasons, and encouraged for suggestive use by those addicted to onanism.
Just as we are charged by Christ to choose either God or Mammon, and we are warned not to make the mistake of trying to serve two masters, in the area of marriage, we must choose either generous fruitfulness or planned sterility.
I do not see how you can square this philosophy of condemnation of family limitation with the marriage of St. Joseph and the Blessed Virgin, which was based on that very premise of planned sterility from its beginning, or with the practice of the early Church of imposing marital continence on married major clerics in Holy Orders who then accepted planned sterility.
Frustrating the primary purpose of marriage is not a morally acceptable ends.
This would make St. Joseph and the Blessed Virgin sinners, since they purposefully and with forethought thwarted the primary purpose of marriage in contracting their marriage. Similarly, many saints in the early Church contracted such marriages to avoid punishment for the pledge of continence. This condemns them also.
Comparing the Holy Family to NFP seems sacrilegious to me. The big difference, first of all, is that, as her name implies, the Blessed Virgin Mary was a VIRGIN. St. Joseph also was celibate, at least during his marriage to Mary. They didn't have sex. Virginity is a higher calling. But users of NFP want to have sex but just not have children, thus frustrating the nature and purpose of the conjugal act.
Here's a simple suggestion: any Catholic couples who feel they have grave reasons to avoid conception could simply imitate the Holy Family and avoid all marital relations until they are ready once again to conceive. This would completely eliminate the need for thermometers, beads, charts, graphs, etc.
Hermann: "This would make St. Joseph and the Blessed Virgin sinners"
I hate to break it to you, but they were sinners. They needed the atoning blood of Jesus Christ just as much as you or I....