[xyzzy123]

Agree, it's not possible to create something like sars-cov2 completely de-novo. I assume this is what you mean? Claims of impossibility here need to be quite specific to be meaningful, I think.

On the other hand if you have not read the DEFUSE proposal you are in for a real treat. It is absolutely plausible that sars-cov2 could be an output of this line of research.

We also don't really know what backbones they had.

[notahacker]

At the other end of the scale, it is absolutely certain that if humans started with a virus more similar to SARS-COV-2 than any publicly disclosed virus and made some possibly very minor modifications they could end up with COVID-19, whether the virus leaked was more or less harmful than its all-natural ancestors.

But if we're looking at specific claims about applied research apparently featured in the book: that it was [most] plausible details like the spike binding to ACE2 receptors were the product of human ingenuity applied to RATG13, the likelihood of this seems to have been undermined by the subsequent discovery of other naturally occurring viruses more similar to SARS-COV-2 already featuring a spike capable of binding to human ACE2 receptors.

Ultimately I guess the question is whether the intermediate viruses between SARS-COV-2 and other variants are more likely to exist in secret in the labs or outside the scope of human knowledge, I guess. I do believe it is possible for virologists to cover up things in their lab especially in this context, but outside the scope of human knowledge is a bigger search space.