If the electron really doesn't exist until you measure it, then why do you get an electron? Let's say you prepare silver atoms as per SG.
We have preparation (oven) where we claim we produce silver atoms. If the atoms coming out of the oven do not exist, then what does it mean to "prepare silver atoms"? Either something comes out of the oven or nothing comes out of the oven. If you say nothing exists until measurement, then a) there is no silver atom and b) there is no gold atom and c) there is no anything else. Until when?
If nothing exists until the interaction with the SG magnet then why does a silver atom come into existence? Why not a gold atom?
If an electron does not exist, then in what sense is there ever an electron in an experiment? As opposed to a proton, or a carbon atom or a sausage? Why doesn't the measurement intended to measure the spin of an electron find a sausage instead?
Why do we observe properties consistent with a silver atom if the silver atom did not exist until we measured it? The SG appartus does not look specifically for silver atoms. You could fire anything through the magnetic field. Why doesn't the SG apparatus bring a gold atom into existence that presumably goes straight through?