Panspermia?

Maybe, but not necessarily even that. The flow of chemical evolution that leads to carbon-based life is just so highly likely. We see some key molecules just about everywhere we look out there. And various simulations (physical, not virtual) create nucleic acids, amino acids, fatty acids, carbohydrates, etc. So there's no reason to think that the Earth is special.

Something I don't get, people say something along those lines -- that with earth-like conditions, blah-blah, earth-like planets, ... then life!

But also experts claim life only arose once on Earth. So, in a place with perfect conditions, the perfect distance from the sun, the perfect atmosphere, perfect trigger, perfect environmental conditions, life only started once! Doesn't that make it so infinitesimally unlikely that even with millions, billions, of planets with the right conditions we still shouldn't expect abiogenesis to occur.

The same arguments that make for extraterrestrial life surely stand against the uniqueness of anything. We know things that are unique. Seems like it's mostly faith based assertion.

Or an anti-faith based assertion. It’s in many ways much more terrifying if we are, in fact, special.

If we are just one of billions of places that life is going strong then we’ll do the best we can but if we don’t survive the eons who cares.

If Earth is the one and only seed of life, then don’t we have an incredible moral imperative not to wreck things here, and if possible to spread life into the darkness?

Being truly alone in the vast dark is a much scarier idea to live with.

Just curious how can anyone conclusively claim life arose only once? Don't they just say we only have evidence that it arose once?

Maybe it started twice or 100M times but 100% of those times the newly started life was "consumed" in some way by already existing life etc.

Yes, that seems a dubious claim. There's no way to know, except though simulations, how many dead ends there were. What we know is that all existing organisms share basic biochemical features. More or less the same nucleic acids, amino acids, and so on. So other paths arguably got competed out. Or merged, as we know for nuclei, mitochondria and chloroplasts in eukaryotes. Probably also components of bacteria. Flagella, maybe? The whole DNA/RNA/protein thing could well be a kludge.

The especially cool aspect of searching for life elsewhere in the solar system is the possibility that we'll find other variants that dominated.

It's also because we have tried all sorts of approaches for the past 70 years or so and we haven't been able to bootstrap it ourselves.

I doubt that any of the experiments have run for longer than a few years. And probably less.