While from a US political perspective, it may appear that the lab leak hypothesis began with the conspiracy theory that China created a weapon, this is not the dominant perspective among scientists who have expressed doubt publicly (and privately).
Our prior is that novel viruses come from zoonotic sources. We haven't ever experienced a pandemic derived from a laboratory leak. It seems fanciful, because it would be unprecedented. But, what would it look like if it did happen? How would it be any different than what we've seen?
Given the situation, yes, we cannot make any conclusions without evidence. And this implies a burden of proof on governments. The fact that this outbreak began in China is unfortunate, but it does not make it right for them to withhold information on the origins of the virus. They should share every scrap of information and evidence that they have, or expect exactly the kind of reaction that you are critiquing.
There is no fallacy of middle ground here. There is simply a lack of hard evidence to confirm a particular hypothesis about where this virus came from. And, there is an uncomfortable abundance of circumstantial evidence pointing in a highly unusual direction. This is not an issue that you can align with the US political spectrum. And it can be approached without needing to make any claims about how good or bad the Chinese government is. You cannot claim to know what this virus is without information that is not available.
Claims that it is zoonotic are unfortunately just as baseless as any conspiracy theories about weapon development that you've been hearing. The argument for zoonotic origin are based on a single piece of evidence that came out of the labs in the very city where the virus was first found: the sequence of a related SARS-like virus, and one with some very unusual sequence features and publication parameters. Doubt is reasonable. We should fully accept the possibility that humans were able to generate such a construct, and be ready for the next time it happens. The basic fact is that we know how to make such a virus, and that information is now out in the open whether or not this particular virus came from a lab.