Atheism is a mental illness: lazy bake edition

Here is my argument against atheism, continue to read after it because it seems atheists need instructions on how to engage with arguments without shitting their pants:

A1a: we live in a causal universe
A1b: every effect has a cause
A2a: if we follow that chain back far enough we reach “the beginning of our universe”
A2b: If an in-universe cause preceded this, it is not “the beginning of our universe”
Therefore our universe began with an external cause;

B1: premise A1 is foundational to discerning truth through science
B2: premise A2 is a tautology.
Therefore arguing against A requires you to argue against the validity of the foundation of using science to discern knowledge.

Okay so here is how arguing works: you have a couple options:
>Disagree with one or more of my premises
>explain how the conclusions are fallacious

These are your options. Failing to do one of these is tacit agreement that my premises are sound and my conclusions follow from the premises.