???
There are probably lots of reasons not to believe in God, but not wanting to go to heaven doesn't make sense.
The difference is whether those 2 billion care whether the rest believe or not. Christians can warn, testify, show, and pray - but not convert. People have to do that bit by themselves.
I think Paul (or one of the apostles) said once that even if an angel came down from heaven and told people about God, some still wouldn't believe. So the first 30 years of Jesus' life wouldn't change much about your belief anyway - neither would 2 billion, or even 2 Christians.
PS. What do you expect from a gospel thousands of years old? One flawless, irrefutable message? As you know, not even a single word can be irrefutable (love? truth? evil? do they mean to you what they mean to me? Hopw long would one book have be to explain what one needs to know about those words?).
But guess what, there is a message: Love God with all your heart and your soul and everything you have, and love those around you equally. There is also a promise: God will give you love and eternal life.
The problem is that people need more, they need to know history (wars, oral traditions, prophesies - and how God was there), eyewitness accounts, etc. (no written account will give anyone enough proof anyway, but it's the only way to capture it - in words - isn't it?)
How can you expect human accounts about different human experiences over hundreds of years to be consistent? There are so many layers of the Bible - chronological, historical, poems, songs, letters, sermons, accounts, laws - that it's a miracle that there's *any* kind of consistent message at all. And that's why no one can say that they are a Christian if they don't study the Bible and try to find out more and learn from it. You don't just magically become an enlightened saint, and you don't get the message by reading only the parts you like.
What would you like to know?