They pointed out that inferences can also be drawn their way. This is why, among other things, Sola Scriptura is a dangerous superstition.
eeeeeeeeeeeeeeeeeeeeek.
I would say their "inferences" from scripture is a tad more stronger than total speculation from someone 1500 years later.
"Sola Scriptura is a dangerous superstition."
Not as dangerous as relying on expedient tradition interpreted by professionals with a position to protect.
Alright. What Biblical inferences draw your way to show that Mary was a perpetual virgin? A few times BD has given a list of scriptures showing that Jesus had siblings. What scriptures do you offer to show that He did not? It would seem that your best possible argument, one in which every single verse was interpreted exactly as you needed, would be that the Bible is silent on the matter. Nothing that is actually in the Bible really helps you here. The Marian doctrines are (mostly) completely extra-scriptural. That is why our side is the only one that actually HAS Biblical inferences. All your side can do is interpret some verses out of meaningful existence, and then rely solely on extra-scriptural text for the "facts".
Here, Sola Scriptura makes a strong case against Mary's perpetual virginity. If your refutation was based on other scripture, then you would have a case. But it does not appear to be. It appears that it is only based on re-interpreting the "positive" argument in scripture out of existence, and then using only extra-scriptural text to support an alternative "positive" argument. I would imagine that an unbiased observer would find this very unpersuasive if a premise was that scripture was an equal authority. Sola Scriptura is only dangerous to the RCC. :)