often the Atheist will then Move on one of two Supporting Arguments 1. "Evil exists, therefore God Does not Exist" or 2. "The Bible is Flawed, therefore God Does not exist".
Start with Number 2. ....therefore, the Bible is not the word of a god or else that god is flawed.
Back to Number 1. Incredible evil and injustice exist, therefore the wonderful god that people have created does not exist.
All we can do is say that there is no evidence of God. It is not totally unrelated to agnosticism. They say "I don't know" and an atheist says "I see no evidence." Often, it is the (totally conficting) anecdotes that make agnostics unsure. That's as far as atheism can go- NO EVIDENCE.
Science recognizes that it is totally impossible to prove the non-existence of Big Foot, ancient alien astronauts, and Flying Spaghetti Monster.
By your "unscientific" claim, I can freely start a religion based on Big Foot being the descendants of alien astronauts that built the pyramids in order to sacrifice to Flying Spaghetti Monster. You must not say I am wrong because you cannot "prove" such a thing.