Then why is the Big Bang being used in this thread to evidence that abiogenesis must have occurred?
The true believers are having a hard time correlating their thoughts on the topic of the origin of life it seems. The premise set forth in the OP is consistently being validated in this thread.
I disagree, as I'm sure others do. The only marginal relevance this has is that, according to the consensus of modern scientists, at one time there was no life, and later there was life. As a consequence of that, we infer that it is possible that life came from non-life.
Even if somehow this statement turned out to be false, that is the current understanding of "what science says" about the origin of life. It came about as a consequence of organic chemistry.
Modern scientific consensus also says that at some point in the distant past, there was a single cell that was an ancestor of every living thing on the planet today. On that point, there isn't quite universal agreement. Some people think there was so much gene swapping that went on among independently arising similar proto-organisms that it would be impossible to find one single cell which contained ancestral DNA of every single organism on Earth today. So, it might be the case that instead of one single cell that was a common ancestor, there was a pool, or colony, or some collection of cells that shared DNA, and everything else came from that pool or colony, but not necessarily from just one cell.
I, personally, lean toward the one cell theory. In fact, it is highly possible that you could go smaller than that. It may be that there was one, single, molecule.
So, that's what science says. That there may have been one molecule, or one cell, or maybe one small collection of cells, that was the universal ancestor. The OP seems to think that we atheists don't understand that. I'm trying to figure out why DOC thinks that. What is it that he thinks we don't understand?