I am somehow still surprised at how many of my intelligent, educated healthcare coworkers believe in the purposeful bio weapon theory despite there being no evidence of human-made genetic manipulation. We can analyze whole genomes now, there’s no need to make shit up.
What possible evidence would there be to “prove” this negative? Maybe if we happened to find the exact source animal to test? Since that is unlikely, all we have to go is the genome of the virus compared to similar viruses in the wild and similar viruses in published research. And that wouldn’t be proof enough for you.