Please don't confuse "blunt" with "snarky." I just feel that no matter how many times opponents are corrected on this matter, it doesn't do any good. So here it goes:
1. The kalam cosmological argument (KCA) rejects the possibility of an infinite past.
2. The Aristotelian and Leibnizian cosmological arguments (ACA and LCA, respectively) do not necessitate a finite past.
3. When the ACA rejects the possibility of an infinite regress, it's not with respect to a temporal regress of causes. Rather, when the proponent of the ACA denies an infinite regress, it is with respect to a regress of sustaining causes. It's one thing to ask why something began to exist, and quite another to ask why it continues to exist.
I'm amazed at how few atheistic opponents seem to grasp these distinctions, no matter how many times we explain them to them. Take the argument from motion (change in general), for example:
1. Evident to the senses is motion. (Premise)
2. Everything in motion has its motion sustained by another. (Premise)
3. Either an Unmoved Mover exists, or else these exists an infinite regress of sustaining movers. (Implied by 2)
4. There cannot be an infinite regress of sustaining movers. (Premise)
5. Therefore, an Unmoved Mover exists. (From 3 and 4)
I've already addressed the most common objections to the argument from motion, and to this day, I find them exceedingly weak. I've also written extensively about how the divine attributes can be inferred from the Unmoved Mover's existence. My conclusion is that atheists should abandon their atheism in favor of deism or some form of theism.