Oh, absolutely. I wasn't aware anyone had made such a claim. It is certainly a silly argument.
Because the full quote of Luke 1:34 (KJV) is: "Then said Mary unto the angel, 'How shall this be, seeing I know not a man?'". Now, the way I read this is that Mary interpreted Gabriel's words to mean that she was going to get pregnant very soon, prior to her marriage, not that she was going to get pregnant in the normal course of events.
It is an assumption that Mary took the words that way. Nothing in the text claims any time frame for the pregnancy, nor for how far in advance of the marriage the visitation occurred. We don't know if it was a week before the wedding or a year.
If the angel had said "you ARE pregnant" then Mary would certainly have the response she did. But telling an engaged woman that she WILL conceive should not lead to mystification. Unless, of course, she was ignorant of the birds and bees, which I don't think is the case.
"... seeing I know not a man" is present tense, not future tense. Unless there's something funky about the Greek I'm not aware of.
Again, past tense would make more sense. "I have not known a man" If she thought she was to become pregnant at the moment or very soon.
Is she saying "I know not a man" like someone might say "I do not eat meat"?
SD
I'm not claiming that Scripture proves that Mary did have subsequent marital relations, either; while it does refer to "brothers" for Jesus, it seems to do so in a context that admits to (but does not require) the usage of the term to refer to people to whom you are very close, but not related to in blood (such as my fraternity brothers). So, if you want to believe that she stayed a virgin all her life, go ahead. But to insist on it as a matter of doctrine is farther than I think is justified.