I think it's worth noting a few things:

1. most Christians don't believe the Bible should be interpreted literally

2. the Bible's overall message is incoherent, and therefore hard to pin down

3. most Christians haven't actually read the Bible

4. Christianity existed for almost 400 years before the Bible was first compiled

5. the Apostle's Creed - which is perhaps the best and most concise summary of what anyone who calls themself a Christian probably believes - was originally written before the Bible was ever compiled.

So although the Bible has been important in shaping Christianity, it really is by no means definitive. And so if you insist on claiming that the Bible offers a definitive statement on what most - or even a majority of - Christians believe, then I'd say that still amounts to a straw man argument.