It's not a crazy theory by any means, but, if it happened, then there's evidence. So, where is the evidence? Literally, where is there any actual evidence it happened?
Really? Why would there be evidence TODAY? Those bats have likely been destroyed, and all records of sequences taken from them have likely long since been shredded and burned.
There's not that much evidence involved here.
Are you asking me to believe a theory for which all the evidence was either not uncovered or destroyed? Why is that more plausible than origin from outside the lab?