Gearhead wrote
The only generally accepted exception to this rule seems to be extraterrestrials, evidence for whom is non-existent yet most people readily accept they are out there :?
The difference there is plausibility. It would be an enormous surprise that among trillions and trillions of stars, with trillions and trillions of planets, that life began and evolved only once in the 14 billion years that the universe has existed. Any scientist would admit the possibility that life on earth is unique, but they'd also point to ongoing research into the origins of life on this planet that hints that it isn't as unlikely as previously thought. Another example would be the existence of planets outside the solar system. They were widely believed in before ever being detected. It was no surprise that they were found, because their existence was so plausible.
Plants trying to remember whether they sent their aunt Martha a christmas card, however, would mean rewriting everything known about botany and biology (which scientists would not resent doing, but only if there was massive, compelling evidence - as happened with Newton's mechanics, Darwin's theory of evolution, Einstein's theory of relativity, and the theory of tectonic plate movement, to name a few).
It's worth acting like you believe in things that are plausible - like taking out insurance against your house burning down, or planning a contingency for a major earthquake. Not worth acting like you believe in things that are wildly implausible - like putting out food for the fairies.
