https://www.documentcloud.org/documents/21066966-defuse-prop...
So is it really that crazy to think they made a chimera of two "random isolates"? David Relman didn't think so:
> This argument fails to acknowledge the possibility that two or more as yet undisclosed ancestors (i.e., more proximal ancestors than RaTG13 and RmYN02) had already been discovered and were being studied in a laboratory—for example, one with the SARS-CoV-2 backbone and spike protein receptor-binding domain, and the other with the SARS-CoV-2 polybasic furin cleavage site. It would have been a logical next step to wonder about the properties of a recombinant virus and then create it in the laboratory.
https://www.pnas.org/content/117/47/29246
Of course the opportunities for a lab accident aren't limited to genetic engineering. SARS-CoV-2 could be a naturally-evolved virus, but one that was sitting harmlessly in a remote cave until WIV researchers collected it. SARS-CoV-2 could also be naturally-evolved, and spread to some hapless villager who then made a day trip to Wuhan; but the point is that we don't know, and all options require investigation until we do.