Why atheism always has a burden of proof

[Gilgamesh]

Okay, so you affirm my statement of (b), that an atheist must also affirm that "atheism is more rational than theism", or at minimum, "atheism is rational."

"b) the claim that atheism is a more rational position than theism" is not a claim that I put forward and indeed wouldn't be entirely correct in and of itself. However, atheism is a more rational position than theism in the event that the atheist is given a claim by a theist, but the claim goes unsupported. The atheists lack of belief, in that event, is rational.

You're saying atheism is rational and theism is irrational because no evidence has been presented for theism?

The position of atheism, yes; the lack of belief in the theists god claim.

How does that reasoning work, for, say quantum mechanics? "Prior to sixth grade, I saw no evidence for quantum mechanics. So quantum mechanics became rational in the sixth grade".

The concept didn't become rational in the sixth grade, but it only became rational for that person, in particular, to believe the concept in the sixth grade. Belief in quantum mechanics becomes rational for one when one sees support for the claims within quantum mechanics.

Good day.