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.