As said, we will never agree on this issue, but consider the following:
There are a number of passages in the New Testament that argue against the dogma of Marys perpetual virginity. Note the following:
Matthew affirms that Mary was found to be with child before [she and Joseph] came together (Mt. 1:18). The term came together (from sunerchomai) includes the idea of sexual intimacy (cf. 1 Cor. 7:5; see Danker, 970). The implication clearly is that ultimately, they came together. H.L. Ellison comments that the construction is incompatible with the doctrine of the perpetual virginity of Mary (1188).
Matthew declares that Joseph knew not (i.e., was not sexually intimate with; cf. Gen. 4:1) Mary until [heos hou] she had given birth to a son (1:25). While the expression heos hou does not absolutely demand that Joseph and Mary were intimate after Jesus birth, that would be the normal conclusion, unless contextual considerations indicated otherwise (cf. 2 Sam. 6:23). In fact, elsewhere in the New Testament (17:9 24:39; cf. John 9:18) the phrase (heos hou) followed by a negative always implies that the negated action did take place later (Lewis, 1.42). There is no valid reason why Matthew 1:25 should be the exception.
In Luke 2:7, Jesus is called Marys firstborn child. While the term prototokon does not demand unequivocally that Mary had other children, this term most naturally suggests that she did (Geldenhuys, 103). If the sustained virginity of Mary is such a crucial theological point, why did not Luke simply say that she brought forth her only son? That certainly would have settled the issue.
There are several passages that mention the siblings of Jesus (Mt. 12:46ff; 13:55-56). Catholic apologists appeal to the fact that the term brother (adelphos) is sometimes used in a broader, kindred sense, e.g., cousins. While adelphos (which literally means, out of the same womb) is employed loosely on occasion in some literature, in the New Testament adelphos is never used for a cousin. The word anepsioi signifies that relationship (cf. Col. 4:10).
Moreover, Jesus is said to have had sisters (Mt. 13:56 - adelphe). Why should it be assumed that Matthews use of mother was literal, but that the terms brothers and sisters were used figuratively? If sister is literal in Acts 23:16 (Pauls sister), what would compel one to view the same term in a different sense in Matthew 13:56? Terry notes: It is an old and oft-repeated hermeneutical principle that words should be understood in their literal sense unless such literal interpretation involves a manifest contradiction or absurdity (159).
The alleged perpetual celibate state of Joseph and Marys relationship is contrary to the divine ideal. Marriage, as designed by God, was intended to bring a man and woman together as one flesh (Gen. 2:24; cf. Mt. 19:5-6). Subsequent to the initial physical bonding is the responsibility to render to one another what is due these terms expressing a sacred obligation (1 Cor. 7:3). If there is to be abstinence, it is to be by mutual concession, and that only temporarily (v. 5).
Moreover, many scholars have opioned that the "perpetual virginity" theory had its roots in the pagan environment of the post-apostolic age when there was a strong emphasis upon celibacy within certain heathen religions. In that day, sexual intercourse, even within marriage, sometimes carried the suspicion of sin.
In fact, Alexander Hislop has shown a remarkable concurrence between the Vestal Virgins of pagan Rome, and the propensity for virginity that evolved in the digressive church of the post-apostolic period (Hislop, 223, 236-238, 250).
Most suspect, that the Roman Church was attempting to accommodate Christianity to paganism, in order to provide a comfort zone that would attract the heathen to the religion of Christ. This is an historical reality that not even Catholic scholars deny (see Attwater, 363). For an historical survey of this phenomenon, see Edward Gibbons famous work, The Decline and Fall of the Roman Empire (Chapter XXVIII). Gibbon concludes this chapter with these words:
The most respectable bishops had persuaded themselves that the ignorant rustics would more cheerfully renounce the superstitions of Paganism, if they found some resemblance, some compensation, in the bosom of Christianity (II.70).
When I hear the RCC tone down its assertion that prayers to Mary are required of their followers in order to obtain absolution (as if the Eucharist were not enough!), then I might be willing to hear what the RCC has to say about Anglicans and their view of Mary.