And let's not even begin to think what will happen if there were to be evidence that this was an intentional release.
A similar, though obviously still very different, example that came to my mind is Chernobyl. The incident made bad reactor designs and their consequences visible to all, and in the long run, it improved nuclear reactors' safety. How would you feel that after Chernobyl, there was no research on why it happened, and people would have said "well, what's happened happened, there is no way to change that, so why investigate"?
If we never figure out (and we don't even attempt) how the virus came to be (wet market, lab accident, intentional release, eating raw exotic animal, or just a normal mutation, I don't know, I'm not an expert, but saying the options I heard so far), the same circumstances will be continue to be available, and sooner or later, another (potentially worse) pandemic will hit us.
However, as you mentioned, there are negative effects of knowing things, so I wish whenever we do find out what and how happened, nations could do a "blameless post-mortem" (in case it was unintentional).