What possible positive outcomes are there?

I think one main reasoning goes like this: basic research about your enemy is often time very well spent.
There are quite a few pathogens out there that would be extremely bad if they figured out just one or two more tricks.
How to go airborne, for example, or how to attach to human cells. Or related things, like how and when certain families of viruses mix and combine.
Learning how those mutation mechanisms work and combine could help in a lot of ways, for example determining which "not quite there yet" diseases are the biggest risk and might warrant preventative action.

Much of the research is valid, and I believe it can be done safely, given the right care.

That care is not always taken, alas.
It is sadly true that lab leaks are not exactly unheard of, ignoring any discussion of Covid19.

Jim