Why are Protestants, who believe in Scripture, so convinced that Mary had other children?

They are not inspired by love for Christ, or for the mother of Christ, or for Scripture in their doctrine. Their main desire is to maintain a doctrine differing from that of the Catholic Church. But it is a position, which is rapidly going out of fashion. Learned Protestant scholars to day deny as emphatically as any Catholic that Mary had other children. When Our Lord, dying on the cross, commended His mother to the care of St. John, He did so precisely because He was her only child, and He knew that Mary had no other children to care for her. The idea that Mary had other children is disrespectful to the Holy Spirit who claimed and sanctified her as His sanctuary. It insults Christ, who was the only begotten of His mother even as He was the only-begotten of His Heavenly Father. It insults Mary, who would have been guilty of great ingratitude to God, if she threw away the gift of virginity, which God had so carefully preserved for her in the conception of Christ. It insults St. Joseph. God had told him by an angel to take Mary to wife, and that the child to be born of her had no earthly father but was the very Son of God. God merely gave St. Joseph the privilege of protecting her good name amongst the undiscerning Jews, and He chose a God-fearing man who would respect her. Knowing that her child was God Himself in human form, Joseph would at once regard her as on a plane far superior to that of any ordinary human being, and to him, as to us, the mere thought of her becoming a mother to merely earthly children would have seemed a sacrilege.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty