no it's not. it might be impossible to prove the negative, but if it did come from the lab there should be physical records and first hand witnesses.
> so what
so maybe we make it a point to have the lab shut down so this doesn't happen again? maybe we publicly acknowledge there are secret teams working on secret science and viruses that can kill people en masse?
but you have a point, it's always easier to embrace nihilism than tackle hard problems head on.
However we ended up unbanning it and we still do it now. If the goal is to simply stop this type of research in its entirety, there's still no point of trying to get China to stop as we have no authority in China (or any other country) to begin with. Even if China were to claim they've stopped we have no way of knowing.
Let's just assume China did have a lab accident. OK, then what? We tell them to stop doing it? Let's say they agree. In the future they decide to start doing it again. The entire thing is pointless to begin with. We can't get our own citizens to consistently wear masks and we think we're going to substantially change China's behavior here - hilarious.
It's pretty absurd to say that it makes no difference whether or not the virus was a lab leak or not. The answer to that question changes the posterior risk estimates of such research and therefore our international funding and domestic regulatory priorities.
There's also such a thing as soft, diplomatic nudges. Not everything is "force X to do Y when they want not-Y".