Here is the counter argument, courtesy of
http://www.totustuus.com/virgin.htm
Mary's Perpetual Virginity
by Jim Seghers
There are four arguments against Mary's perpetual Virginity. First, "until" in Matt 1:25 seems to imply that Mary and Joseph had marital relations after the birth of Jesus. Secondly, according to both the Old and the New Testament sexual intercourse for married couples is divinely approved (Gen 1:28, 9:1, 24:60; Prov 5:18; Ps 127:3; 1 Cor 7:5, 9). Third, we are told that Jesus had brothers and sisters (Matt 12:46-47; Matt 13:55; Mark 3:31-32; 6:3; Luke 8:19-20; John 2:12; 7:3, 5, 10; Acts 1:14). Lastly, Jesus is called Mary's "firstborn" (Luke 2:7).
Argument # 1. "Until." The problem with this understanding is that it forces a modern English use of until on the Bible. In the Bible the Greek and Hebrew words for until means only that some action did not happen to a certain point. Scholars are in agreement on this point. For example, Dr. William Hendriksen, the former Professor of New Testament Literature at Calvin Seminary in Grand Rapids, Michigan writes: "This conclusion cannot be based merely upon the negative plus "until." That wording does not always introduce an event (in this case: she gave birth to a son) whereby the earlier situation (the couple had no sexual relations) is reversed (they now begin to have sexual relations)." From The Gospel of Matthew, p. 144.
Consider this quotation from Samuel: "And so Saul's daughter Michal was childless until the day of her death (2 Sam 6:23)." Are we to conclude that she bore children after her death? How about the raven released from the ark? We read that the raven "flew back and forth until the waters dried off from the earth (Gn 8:7)." Does that mean the raven returned? Other examples can be seen in Dt 34:6; 1 Macc 5:54 and Ps 109:1 [RSV 110:1].
Argument # 2. Sexual intercourse for married couples is divinely approved. All Christians agree that intercourse between married couples is divinely approved. However, the fact that marital intercourse is divinely approved does not mean that it is divinely commanded. Nor can it be argued that because it is approved, Joseph and Mary fulfilled that marital right.
Argument # 3. The "brothers" of the Lord. Neither Aramaic, the language Jesus probably spoke, nor Hebrew has a separate word for cousin. In reality the term, brothers, was commonly used in the Bible to describe close family members including cousins and uncles. Lot, for example was Abraham's nephew. He was the son of Abraham's brother Haran. Yet in Genesis 14:14, Lot is depicted as Abraham's brother. In Mt 29:15 Jacob is called the brother of his uncle Laban. Again in 1 Chron 23:21-22 the daughters of Eleazar married their brethren. This is not possible because Eleazar had no sons. These brethren were really their cousins, the sons of Cis. Cis was Eleazar's brother.
We learn from other Biblical passages that the word brother even had a broader use. In the case of the forty-two brethren of King Achaziah (2 Kings 10:13-14), the expression is used to refer to mere kinsman, not even close relatives. Similar uses are found in: Dt 23:7; Jer 34:9. Brother was also used to describe unrelated people, such as a friend (1 Kings 9:13, 20:32; and 2 Sam 1:26). In Amos 1:9 the word is used to describe an ally.
In the passages that refer to the brothers of the Lord, Mt 12: 46-47, Mk 3:31-32, and Lk 8:19 all seem to be relating the same incident. The use of the word brothers, as we have already seen, is not persuasive that Mary had other biological children.
Specific brothers are named in two passages. In Mt 13:55 James and Joseph and Simon and Judas are listed. James and Joseph are identified in Mt 27:56 as the son of another Mary, probably Mary of Clophas found in Jn 19:25. Simon appears to be Simon the Cananean of Mt 10:4. Judas is called the son of James in Lk 6:16 and Acts 1:13.
The second listing of brothers occurs in Mk 6:3. They are James and Joses and Judas and Simon. James and Joses are identified in Mt 15:40 as the sons of another Mary. This is probably the same Mary discussed above who appears in Jn 19:25. Judas and Simon appear in Matthew's list (Mt 13:55).
Argument # 4. Firstborn son. This objection ignores the ancient Jewish idiomatic use of the word firstborn. This term clearly refers to the first child who opens the womb (See: Ex 13:2 and Nb 3:12). The Mosaic law commanded that the firstborn son be sanctified (Ex 34-20). Are we to suppose that parents had to wait until a second son was born before they could call their first son the firstborn, and only then were obligated to carry out the Mosaic provision? This was clearly not the case.
Conclusion: There is no Biblical evidence that indicates Mary had any other children after the birth of Jesus. However, the above discussion does not present a Biblical case for Mary's perpetual virginity. What is that Biblical basis?
Biblical Basis for Mary's Perpetual Virginity.
Position # 1. At the Annunciation Mary question, "How can this be" (Lk 1:34) makes no sense except in the concept of a vow of lifelong virginity. This is the understanding from the earliest interpretations of this passage. Mary and Joseph were betrothed, that is, legally married at the time of the Annunciation. It's hardly sensible to suppose that Mary's question was an inquiry regarding the biological process of how children were conceived.
Position # 2. A second Biblical argument that supports the traditional Christian belief in Mary's perpetual centers around the account of Jesus being found in the temple at age twelve (Lk 2:41-51). There is no hint of other children.
Position # 3. In the passages that refer to Jesus' brothers, the sacred authors are careful to only call Jesus the son of Mary, no one else. Additionally, in referring to Jesus as "the son of Mary" (Mk 6:3), the force of the Greek implies that Jesus was Mary's only son, not a son.
Position # 4. In the Jewish society in which Jesus lived, younger sons never gave public advice to an older brother, much less, the oldest son. This would be very disrespectful. Yet, we find Jesus' brethren advising Jesus to leave Galilee and go to Judea to make a name for himself (Jn 7:3-4). Similarly, at another time his brethren attempted to restrain him saying: "He is out of his mind (Mk 3:21)." These passages are understandable if these brethren were in fact Jesus' uncles.
Position # 5. Lastly, Jesus' action at the foot of the cross, when he entrusted his mother to John, makes no sense if Mary had other sons (Jn 19:26-27). The social customs of the time would have made such an action unthinkable.
Patrology
(All references are to: The Faith of the Early Fathers, edited and translated by W. A. Jurgens (The Liturgical Press, Collegeville: Minn, c. 1979), III Vols.
St. Athanasius (358-362) in his Discourse Against the Arians called the Mother of Jesus, "the ever-virgin Mary" #767a, I, p. 330.
Didymus the Blind (381-392 - He was head of the catechetical school at Alexandria) "for neither did Mary. . . marry anyone, nor did she ever become the mother of anyone else, but even after childbirth she remained always and forever an immaculate virgin." #1073, II, p. 62.
St. Epiphanius of Salamis (374) "the holy ever-virgin Mary" and "to Holy Mary is invariably added, for that Holy Woman remains undefiled." #1111, II, p.76.
St. Jerome (383) wrote a whole treatise called: Against Helvidius: The Perpetual Virginity of the Blessed Virgin Mary, II, pp. 190-192.
St. Augustine (391-430) "a virgin conceiving, a virgin bearing, a virgin pregnant, a virgin bringing forth, a virgin perpetual." #1518, III, p.30; also: #1642, III, p. 71; #1974d, p. 166.
Leoporius (426) "the ever-virgin Mary" Document of Amendment, #2048, III, p. 197.
St. Cyril of Alexandria (542) "Therefore he kept His Mother a Virgin even after her childbearing." #2133, III, p. 232.
St. Peter Chrysologus (405-450) "and a virgin she remained." # 2177, III, p. 267.
Leo I (c. 461) "a Virgin conceived, a Virgin bore, and Virgin she remained" III, p. 275, #2194.
Gregory of Tours (575-593) "A virgin both before and after she bore Him" III, p. 306 # 2288 b.
Sophronius of Jerusalem c. 638 "the immaculate virginity which was unblemished before the birth, during the birth, and after the birth" III, p. 307 #2289.
John Damascene c. 743 "The Ever-Virgin remains after birth a Virgin still." III, p. 340 #2372.
The Reformers
LUTHER wrote on February 2, 1546 that Mary was "a virgin before the conception and birth, she remained a virgin also at the birth and after it."
ZWINGLI wrote in January of 1528: "I speak of this in the holy Church of Zurich and in all my writings: I recognize Mary as ever virgin and holy."
CALVIN in his Commentary on Matthew called those who interpret the gospel (Mt 1:25) to imply that Mary had other children as "pig-headed and stupid." Later, commenting on Mt 13:55, he wrote: "we have already said in another place that according to the custom of the Hebrews all relatives were called "brethren."