Isn't the whole idea or rule of "burden of proof" equally as much man-made as atheists claim the Bible is?
Why should I follow YOUR man-made rules instead of any other man-made rules?
Let's pretend for the sake of discussion that I believe in Unicorns.
Can you prove me wrong? Can you prove to me that Unicorns don't exist? Of course not! You can't prove a negative. All you can do is point out to me that there is no evidence to show that Unicorns exist.
If I were to continue to insist that they in fact do exist, wouldn't you reasonably ask me to provide evidence for my claim?