Will some of you, perhaps at least one Catholic and at least one Protestant, please explain to me why it actually makes any difference at all whether Mary had children after she gave birth to Jesus?
If she DID, that doesn't make her any less of a virgin when she conceived and gave birth to Jesus Christ, our Lord and Master, nor would it have made her any less "Holy". And of course, if she did NOT have other children, then the same is still true.
But as a Catholic (though fallen-away by not attending Mass), let me add a point that I seem to sometimes perceive when debating (or reading about) this issue. Although I must admit that it has been very rare, still there have been a few times when I have sensed some degree of hostility, if you can believe it, to the Virgin Mary herself, coming from some of the opponents to her perpetual virginity. Why? Do those who feel that way somehow think that Mary is now evil, because they think that Catholics worship her and that this somehow makes her a false god? Do they think that Mary is somehow the 'harlot of Babylon' mentioned in Revelations? What is the deal? In conjunction with their claim that Mary could not possibly have remained a virgin because of what is said in Matt. 12:46 -- "While He was still speaking to the crowds, His mother and His brothers appeared outside, wishing to speak with Him." -- many are very quick to follow-up with verses 48-50: "But He said in reply to the one who told him, 'Who is My mother? Who are My brothers?' And stretching out His hand toward His disciples, He said, 'Here are My mother and My brothers. For whoever does the will of My heavenly Father is My brother, and sister, and mother.'”
It is almost as if they think (and maybe they DO) that this somehow indicates that Jesus had turned His back on them for some reason such as unbelief in Him, and that this further diminishes the holiness of our 'Holy Mary'. Come on, folks, if any of you think that way, I have a few words for you. First, that would be a completely unwarranted supposition because it is quite likely that Jesus was merely using that announcement of their presence as an opportune time to make a true and valid point -- that we believers are His family, too -- and it is also unwarranted because He might well have gone to greet them immediately after making that statement (and which would not be significant enough of a fact worth mentioning in the gospel). There is not the least bit of hard evidence that Jesus was 'dissing' (disrespecting) His family in any way; in my opinion, it is not even suggested in the slightest way. And it would have been equally ridiculous to expect Jesus to have said: "Oh, you mean my STEP-brothers ...", or to expect the gospels to have necessarily recorded that, even if He had. That's because we all realize that only an extremely small amount of what Jesus said during His ministry was capable of being included in a single volume book. But yet I often sense that 'insinuation' of some sort of a divide between Jesus and His family, and that Mary was therefore no longer "Holy" and any more worthy of our veneration and respect than any ordinary person. In fact, to further support that supposition by those critics, I seem to recall such people referring to Mark 3:21 -- "When His relatives heard of this they set out to seize Him, for they said, 'He is out of his mind.'” (NAB). [The KJV says: "And when his friends heard of it, they went out to lay hold on him: for they said, He is beside Himself.'"]
Now, let me make an argue why it is ridiculous to contend that Mary, or Jesus' family, would be unbelievers in Him. First, Mary knew from the moment of her conception of Jesus, that He is the Son of God; did she have a lapse of memory or later believe that it was all a dream? She even approached Him at the wedding feast of Cana with absolute confidence that He could somehow miraculously save the day; ... or did she expect him to take a cart and go buy wine somewhere? Of course Mary knew that Jesus had a mission, and even after Jesus told her explicitly that His time had not yet come, she still ... with confidence that her Son would help ... told the servants to do whatever He told them. And surely by then, she had also heard the stories about Jesus' miracles -- and though many others might have thought that they were just myths or exaggerations, surely she knew differently. So it is preposterous to think that Mary would have EVER been an unbeliever in her Son, or that she would have ever done anything to merit His disdain -- as if Jesus would ever ignore and disrespect His mother inasmuch as Jesus expressly mentioned the commandment: "Honor thy mother and thy father." Jesus said precisely that in response to the question of what one must do to be saved, in Mark 10:19 (NAB): "You know the commandments: ‘You shall not kill; you shall not commit adultery; you shall not steal; you shall not bear false witness; you shall not defraud; honor your father and your mother.’” Surely Jesus honored His mother all of the days of His life, right up to the moment that He spoke to her and St. John while he hung on the cross.
Likewise with St. Joseph (although he wasn't alive during Christ's ministry). He was certainly aware of the divinity of Jesus; besides what Mary told him, he had confirmation when he was told to take the Holy Family into Egypt.
Now, as for any siblings of Jesus, whether they were half-siblings or step-siblings, they would have been raised by Mary and at least part of their lives by St. Joseph; Holy Mary and St. Joseph were both well aware of the divinity of Jesus. Isn't it likely that the siblings of Jesus would have been raised with this same knowledge and awareness -- or if not raised with it, at least told of it by Mary after Jesus began His ministry.
Anyway, one of the ancient books that never made it into the Bible describes the relationship/circumstances between Mary and Joseph this way, in short: Joseph was 80 years old when he became betrothed to Mary, and already had children (probably ALL of the so-called brothers and sisters of Christ, who therefore would have really been STEP-siblings, NOT born of Mary). Because of his advanced age, and perhaps more so because of devotion to God and some divine guidance, St. Joseph never engaged in sexual relations with Mary. There are other reasons why Catholic Church dogma -- much of which is based upon earliest Christian tradition (people who lived at the time and had first-hand knowledge) -- hold that Holy Mary remained a perpetual virgin. But if the Catholic Church happens to be wrong on that point, I ask again: "What difference does it make?"
May the Lord be with you!