The mutations on covid 19 are Really Different compared to the known and studied viruses. If it was a lab leak of an engineered chimera, you'd be able to see that A proteins came from virus X and B proteins came from virus Y and Z, but that hasn't been shown to be the case. From what I understand there are a bunch of smaller mutations across a lot of proteins resulting in something that doesn't really line up with known and studied genomes.
This paper actually goes through and compares the DNA of covid 19 against several other studied viruses: https://www.nature.com/articles/s41579-020-00459-7
I guess I don't find the argument "we can't figure out how to reconstruct SARS-COV-2 from known viruses" very convincing on either side.
Sitting in a cave somewhere implies not being studied, right? Which is more the "natural mutation" thing.
Sitting in some government lab is a different story and depends on belief in scientific institutions to do science and publish peer reviewed papers and all that jazz.
It doesn't have to be crispr introducing reach mutation.
You don't get there by splicing an ACE2 spike onto an RaTG13 backbone and passing it through a dozen mice. That gives you something that still looks similar to RaTG13 and infects mice.
The ACE2 spike also looks most similar to a previously unknown ACE2-binding spike protein found in malaysian pangolins.
So WIV would have had to have discovered that pangolin spike-protein, kept it secret, spliced it into an RaTG13 backbone, then not used mice but passed it through a species like that had a human-like ACE2 for a decade and millions of animals.
An alternative hypothesis is that Charles Darwin did that experiment.