I think that lawyers are typically very poorly suited to the task of writing laws and they frequently write bad laws, especially when it comes to science. And especially when they introduce their own uninformed bias about the science into the process.

Which particular biases in the international low on bioweapons are you referring to?

The link backs up my original "guess" that the thought process driving this entire argument is that we should entirely avoid precautionary research into pathogens and instead just wait for them to occur and kill us (or just hope they never occur).

Many virologists have warned about this practice for years publicly:

https://www.theguardian.com/world/2014/may/20/virus-experiments-risk-global-pandemic

It is well established that the labs involved 'leak' viruses fairly regularly. This work is a huge disaster waiting to happen, always has been and probably always will be. If you are going to risk the future of humanity on your own fear of what 'might' happen, to the extent that you actually make it happen, then the deaths involved are on your hands and the rest of the world needs to know your intent.

it may not be unreasonable to believe in one "conspiracy theory" that you've researched well. But the more improbable events a person believes, and with less affirmative evidence, the less trustworthy that person's assessment should become.

Whether or not such research constitutes 'gain of function' is purely a legal and scientific question, it has nothing inherently to do with conspiracy or theory.