Atheists, tell me, a Roman Catholic: why should I become an atheist?

[Tonus]

how did existence come into being? Catholics believe God has always been, from eternity to eternity, but how do atheists explain that? Without a supernatural being there from eternity, there is nothingness, how does something come from nothing?

I just want to point out that the flaw in this explanation is that god is not accounted for. Claiming that he is eternal confirms that something as powerful and complex as god --who is often defined as all-powerful and as complex and intelligent as it is possible to be-- can exist without a beginning and simply "always be." If this is the case, then it seems that something far less powerful or complex could also exist without a beginning. Such as a universe that renews itself in a cycle of expansion and contraction, or a bubbling multiverse of realities that constantly spit out new realities through black holes or any of a number of other phenomena that are nowhere near as complex as a god and which are therefore more likely to be the case.

If we reject an infinite regress because we cannot fathom the concept of eternity and can only accept things that begin, then god is a non-starter. He is introduced into the equation with exactly those properties that created the conundrum in the first place. It's the lazy way out.