Micahel,

I am not as well-versed in philosophy as some of my colleagues, so I encourage them to validate this, but I'd point out a few things.

First, I'm not 100% sure I understand the objection to the theistic argument. In this argument, God is defined as the Uncaused Cause. If atheists posit a "cause" that "always existed", they have lost the argument since that's the whole point: An uncaused (= "always existed") cause is, by definition, God. (This argument, called the Kalam Argument, does not attempt to prove the Trinity, omnipotence, or omniscience of God; it just aims to prove that as an Uncaused Cause, God exists.)

But more fundamentally, I'd point out that time was created in the Big Bang, making references to things "always existing before" it rather dicey. You can't use time references to relate to the beginning of the Big Bang, as time itself did not exist before then. Consequently, there is no "before" the Big Bang, nor did anything (strictly speaking) "always exist" before the Big Bang, as this would require the existence of time, which is a reality created by the Big Bang.

That's how I'd respond.