(HINT) it ain't us.
At the time of the Protestant Reformation, Protestant, Catholic, and Orthodox Christians all agreed that Mary was a virgin, not just at the time of Jesus’ birth, but for her entire life. You’ve heard the explanation that "Jesus’ “brothers” were really His cousins? You may be surprised to learn that that was John Calvin’s opinion! Ulrich Zwingli especially emphasized Mary’s perpetual virginity. All three also agreed that Mary is blessed among all women, and that it is right for Christians to honor and venerate her. Martin Luther taught that Mary was born without sin and he continued his devotions to the Virgin Mary until his death."
As time goes on, more and more truth is discarded by those following the oral traditions of their protestant progenitors.
Birth control, divorce, abortion for the "right reasons" all eventually came to be accepted. All happened after the Doctrines about Mary came under attack and were abandoned.