Agreed. There are just too many unknowns. Certainly about how life started here(if indeed it did start here). But even more so about what's out there. There's so much we don't know even about the planets and moons in our own solar system, let alone other star systems. It's only recently we've become able to detect exoplanets in significant quantities at all, and we've still only scratched the surface really. And what we know about those planets is very limited. For most of them we don't know much except their distance to the star and estimated size. For a handful we have some information about their atmospheres, usually only enough to narrow it down to a couple of equally plausible models. It's hard for me to imagine us being able to conclusively detect life on an exoplanet. I think the best we'll be able to do in the next several decades is say we're pretty sure a planet's atmosphere contains chemical compounds for which there's no known abiotic origin. But there will be so much uncertainty there in terms of possible unknown abiotic origins that it would never feel conclusive.