Mod-80, I guess what I am trying to say is that if we can’t detect them, then of what use is saying they exist? For all practical purposes, then, they don’t exist. I mean will you ever get into a situation where it is critical to know that there is a sheid up ahead, and you must take evasive or protective action.
A mashal is the ether. At first scientists believed that light required a medium and that the speed of light was with respect to this fixed ether. After a number of experiments it turned out that the ether could not be detected and that the speed of light did not depend on any fixed frame. So scientists said that ether does not exist. They did not say that it exists but is undetectable and plays no role. Might as well say it doesn’t exist. Easier to work with. Of course if some future experiment shows that light does require some medium (like sound requires air), they will say that it does exist. (But presumably they will require an experiment in which light in one situation cannot propagate, but in the identical situation, only with the addition of ether it can. And there would be some independent way to ascertain that there was no ether in the first, but there was ether present in the second as confirmed by XYZ brand ether-detecting compound.)
As far as the gemaras go, one can say they are not meant literally, but are meshalim for some deeper concepts. I mean is one of the 13 ikkarei emuna to believe in sheidim.
I will note though that in Acahrei Mos on the Sair Lazazel, the Ramban goes into a whole arichus that we bring a korbon on behlaf of a sheid, or something along those lines. He says that those who follow the wicked Greek (Aristotle, probably) who don’t believe in anything they cannot see are arrogant. I wonder if he means that Aristotle was known to be a wicked man for specific sins. I mean if he says that Aristotle was wicked because he didn’t want to believe in what he could not see, I fail to see why that makes him wicked. Don’t we say Ein lo ldayan ella mah sh’einav ro’os? Can you blame somebody for not wanting to accept superstition without proof of its existence?
On the ein lo ldayan topic, imagine if 2 witnesses said we saw Reuven raise his arm with a knife and plunge it into Shimon. But Reuven says, it wasn’t me, a sheid killed him before the knife entered. Or he says a sheid pushed my hand with the knife into Shimon, but the witnesses were not on the madreiga to see the sheid. Would he be patur?