Re: The Virgin Birth
Heath, I think that the issue is that some people (me, and perhaps you) are willing to accept that Isaiah didn't actually mean "virgin," and that the author of Mathew mis-read it, and made up a story about Mary being a virgin in order to back up his claims about Jesus being the Messiah. But for more christians, admitting that one of the gospel authors made up deliberate falsehoods in order to convince people that Jesus was the Messiah would call the whole thing into question. If they lied about that, what else were they willing to lie about? Why believe anything they say, particularly the miraculous stuff, if you've already accepted that they've lied about something already.
Note, in this case, I use the word "lied," rather than "just got it wrong." It's one thing to say the NT authors made an error or two. I think many christians could accept that. But you can't really say that in the case of the virgin birth. The author of Mathew really wanted you to believe that Mary was a virgin. There's the whole story of the angel, and stuff. It's not just a "oops!" moment to put that stuff in if it didn't actually happen. It's a complete fabrication of a miraculous event. It'd be a deliberate and intentional lie if it weren't actually true. And that really calls into question the credibility of anything else they say.
So for most christians (and as a non-christian, I'll agree with them, for whatever that's worth), you either accept that what Mathew said was true, or you have to accept that he was willing to make stuff up out of nowhere just to convince his readers that Jesus was the Messiah. For me, as a non-christian, the latter is easy enough to swallow. But for most christians, that's just not really compatible with their faith. An imperfect gospel-writer is one thing, but a one that deliberately tries to mislead is another.
So I think you can make a good case that Mathew mis-read the verse in Isaiah, and that Isaiah never made any predictions about a virgin birth. I also think you can make a pretty strong case that the verses Mathew points to in Isaiah had absolutely nothing to do with Jesus, and weren't at all intended to. But I think the only way someone can really accept that, is to accept that Mathew was making up miracles. And accepting that really means re-examining everything else he claims as well. I think people should do that, but I think asking them to do that and then still accept Jesus as the son of God is something you'll really struggle to do.
Put another way: sure, it's possible that Mathew lied about the virgin birth, but told the truth about "the important stuff," but why would anyone believe that? If you accept that he lied about the virgin birth, why not suspect his other claims too?