real nerdy here but they way they could explain is that you can turn it on but you can't really use it like a Jedi unless you are Force sensitive. Han used Luke's in ESB to cut open that animal but he didn't wield it like a Jedi. Light sabers wouldn't need that button if all you needed to do is use the Force to light it. The light saber is supposed to be heavy like a sword and can only be really used like Kylo, Rey and Finn used it in the final battle using the Force to hold it up and wield it like they did...