Conversion as Proof of God's Existence

In response to my assertion that anything worthy of belief is something that should atleast be shown or testable, I can imagine someone saying, "But look at the change belief has made in the hearts and minds of countless people. Josh, is this result, or demonstration, not sufficient for you to believe in God's existence?"

In the case of a heart patient, there is little doubt that he would die without a transplant, as there's little doubt that if an operation was performed successfully, he would continue living for some time. However, while a person's life may dramatically change and improve after becoming Christian, there is nothing about the personal changes which demonstrate that a God is waiting for him after he dies. The logic inherent in the argument "His life sucked before becoming Christian. His life became better after becoming Christian. Therefore, Christianity made his life better." is strong as long as nothing else in the person's life changed other than the adoption of a whole new belief system and lifestyle (Christianity). But the argument "His life sucked before becoming Christian. His life became better after joining the churh. Therefore, a God exists and all the claims of the church are true." is so obviously devoid of logic, I need not go on. Again, if a claim is not demonstratable, then a belief in it is a matter of faith. To billions of people, a thing being a "matter of faith" is perfectly fine, if not making that thing somehow better than those things which are proven fact-things which we can act confidently in response to to better our lives, yet things which billions of people choose to ignore in favor of emotionally appealing figments of our ancestors imagination.