In this case there is no smoking gun either way and a natural origin is much harder to trace than lab origin. That lack of absolute certainty, which science is often comfortable working with, leaves room for alternative theories to circulate and attach to those who like the sound of them for various reasons. It is a common human flaw that being aware that an event could hypothetically occur can be mistaken for proof that event actually occurred.
Even if we're 50/50 on the source of the virus, maybe we should still ban or regulate GoF research, and consider banning or regulating some types of wet markets.
As to 50/50 being reason to take large scale regulatory action, would you accept this level of proof to enact any law? That seems a low bar to me.
It would only be a conspiracy theory if there was intent - plenty of room for accident without making it a conspiracy.
Why do you think that? Natural origin should leave closely-related viruses in nature, and animal sampling should find that. Such evidence was found for both the original SARS (palm civets) and MERS (camels) within about a year. For SARS-CoV-2, after about the same time and a much more intensive effort, we're still waiting.
Lab-accident origin is easy to trace only if the people working in the lab disclose everything they were working with. This requires both perfect honesty and perfect knowledge. The WIV did lots of work sampling viruses from nature, in remote bat caves that very few other humans would ever enter--around Yunnan to be clear, about 900 miles from Wuhan--and they could have leaked a novel virus before they even had a chance to sequence it. Of course that's still more likely to imply someone's lying, thus the accusations of "conspiracy theory"; but by that standard every human deception in history is conspiracy theory, including every intelligence operation, every Ponzi scheme, every cheating spouse, etc.
I'd put lab origin and natural origin around equal probability myself, and I'd consider anything between 10/90 and 90/10 reasonable. What would you estimate?
The point is that we should consider both the cost and the benefit of any regulation, in an expected value sense. Cars do kill people, but they also provide transportation that we've judged is worth that cost. But there's little indication that the WIV's (USA-funded!) risky research has delivered any significant benefit--the predicted coronavirus pandemic has indeed occurred, whatever the cause, and has anything from the WIV's work help us deal with that? On the other hand, even a small chance that their work caused this pandemic is a hugely negative expected value.
Long before the pandemic, there was obscure, academic debate over whether certain types of research with potential pandemic pathogens were worth the risk. Even with the evidence available at that time, I believe the 2014 ban was good, and its 2017 lifting was bad; but that debate now that takes on terrible new significance.
Speeding is common (difficult to prevent) and exhibits low downside risk. An intruder in the house is rare and carries an enormous downside risk. Which one is more analogous to the escape of a dangerous virus from a lab?