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If we could leave religion out of it (I know, I know), it's because of the unimaginably large scale and distances that it would be amazing to find any evidence of intelligent life looking out from this planet
If Drake and Fermi could have seen this Hubble image of galaxies in deep space, and still deny the possibility of extra terrestrial life, then, yeah, I'd call it foolish. And anthropomorphic to a fault. Those little specks are not stars, they're galaxies.
But they knew this in terms of scale, if not a picture montage. These guys didn’t deny the issue, they just rationally asked “well, where are they?”. You state the scale IS the reason why we can’t prove ET life- so it becomes a tautology- proving itself by being unproveable? I think my math instructors would chastise that point of view. My logic profs would indeed!
Regarding religion being left out, - sorry but evolution is the religion that makes all of this so utterly unproveable-a foundational (error) that just has to be carried through or else the whole house falls....
Just what if all of this creation indeed is not billion or trillions, but only tens of thousands of years old- that order of merit would change the whole metric of the equation- none of the other variables Drake and Fermi etc described would even be reasonable, so the thought, no, the demand, that life exists elsewhere could be moot.
Regards