Suppose the year is 1770 and I am a sailor on one of Captain Cook's expeditions. A fellow sailor breathlessly tells me about the advanced civilizations with flying machines we might encounter, reasoning that such constructions are theoretically possible according to science and extrapolating from extant technology. I'd tell him that I expect nothing of the sort.
I'd also concede that such technology might one day be created: " This might one day change if we become a post-biological civilization, but so far not a single example of such has ever been seen."
So far? No evidence for it. So far, it's only science fiction.
In that case your conclusion shouldn't be that civilizations are only biological. Your conclusion should be: because we have not observed life outside Earth, the more likely thing is that there is not life outside Earth, not that it's biologic.
But I think that you are using correctly your likelihoods but forgetting your priors. The prior in this case is: there is no reason that we know for this not to happen, so, it has to be happening somewhere.
Suppose the year is 1770 and I am a sailor on one of Captain Cook's expeditions. A fellow sailor breathlessly tells me about the advanced civilizations with flying machines we might encounter, reasoning that such constructions are theoretically possible according to science and extrapolating from extant technology. I'd tell him that I expect nothing of the sort.
I'd also concede that such technology might one day be created: " This might one day change if we become a post-biological civilization, but so far not a single example of such has ever been seen."
So far? No evidence for it. So far, it's only science fiction.