Your argument will fall on deaf ears simply because very few people understand how electricity (and, by extension, electronics) work. At best you will get a, "but I'll turn off the Wi-Fi," because they don't understand that varying electric currents can produce spurious noise in nearby circuits.

I'm not claiming that the dangers are real. Modern devices are very low power and very high frequency, so it should be possible to design instruments for aviation that filter that noise out. On the other hand, there are so many electronic devices out there that it is (as you suggested) impossible to test everything independently.