When it comes to SARS-COV-2, anyone who wasn't actually working on the virus in the lab, who says they know for sure it either did or didn't come out of a lab, can immediately be written-off as unreliable. This is because if there were people who were working on it in the lab, then they are the only people who could know for sure. Fauci certainly can't know for sure.
To compound the problem, assuming SARS-COV-2 was the product of a virology lab, that still doesn't mean the virus responsible for COVID-19 originated in the same lab. Other labs, or as unlikely as it may seem given the evidence, nature itself could still be responsible for creating an identical virus. The fact is, right now, nobody knows for sure unless there are virologists who worked on it in a lab and know how it got out.
Personally I believe it likely that there are ( or were ) such virologists. But we have not heard from them in-person. Even if we did, given that the lab in question was run by the CCP, could they be trusted? I don't think so, at least not so long as they're under CCP jurisdiction and control. We have to rely on the best available evidence combined with reason, and that appears to weigh heavily in favor of virology rather than nature.