So, except for the fact that you must believe WIV did all these experiments in total secrecy (so that nobody outside heard of it while visiting, etc) and now won't admit to having done them, it's not a conspiracy theory.
And again, RaTG13, the closest known relative of SARS-CoV-2, was sampled by the WIV in 2013 and published only post-pandemic. So it's unquestionable that they had at least one unpublished virus similar to SARS-CoV-2 in their collection; the only question is how many others.
It's likely that the only people who know the answer are under the physical control of the Chinese government. Even if they're sometimes briefly abroad, they likely have loved ones behind. So it doesn't take any voluntary conspiracy to keep them quiet, just a direction from a government that has amply demonstrated e.g. in Xinjiang its willingness and ability to punish anyone who discloses its secrets.
As I mentioned earlier, a proximal animal host would greatly increase my confidence that SARS-CoV-2 originated from natural zoonosis. Is there any evidence short of a direct admission from the WIV that would decrease yours?
Finally, Marc Lipsitch and David Relman are Harvard epidemiology and Stanford microbiology profs respectively. I'd rather people engaged seriously with the evidence than just relied on credentials; but are you saying they're conspiracy theorists too?
And you are making a claim about them lying, this comes unavoidably from saying that the VIW is the origin of SARS-CoV-2 as the VIW themselves are publicly claiming they have nothing closer than RaTG13.
I noted above that the WIV had a database of viral genomes. Public access to that database was removed in September 2019. They say this was due to repeated hacking attempts. They've taken no steps to restore access, or to make the database available in another format (e.g., a dump on a flash drive) that would clearly present zero information security risk. Do you believe their explanation?
And for emphasis, I don't think it's certain that they're lying (about RaTG13 being the closest known relative, at least; I can't see how anyone with the slightest domain knowledge would believe the "hacking" claim), just as I don't think it's certain that a company is lying about their financials when I want to see audited results. The point is that I don't know, and it's normal for people making an important claim to actively want transparency, to build confidence so people don't have to trust them. The WIV's behavior here is the opposite of that.