So, you do admit that there is absolutely nothing in scripture that discounts Mary's perpetual virginity?
Why should it matter? What matters is that Mary was a virgin when Jesus was born.
We might get some insight into the matter, for those for whom it's an issue, from Matthew:
Matthew 1:24 Then Joseph being raised from sleep did as the angel of the Lord had bidden him, and took unto him his wife:
Matthew 1:25 And knew her not till she had brought forth her firstborn son: and he called his name JESUS.
Could you see how the above passage would be a teeninesy bit suggestive?
On the contrary, I think there is a great deal in scripture that discounts Mary's perpetual virginity. I believe Calvin, Luther and a host of other people were wrong on the matter. I believe there are good reasons as to why they were wrong, but they were wrong nevertheless.