On the one hand, yeah. Worrying about stuff that you have barely any control over won’t get you far. But on the other hand, that guy’s vote counts as much as yours. And if he already believes such silly conspiracy theories as the flat earth theory, he will be easily swayed by whoever is the loudest contrarian.
Iceland and Norway aren’t joining, because they want to control their waters and fishing permits. They still implement all EU regulations not touching those. Switzerland has a weird fetish about being neutral, which currently is just a code word for being the EU’s tax evasion haven. Through agreements with the EU, they too adhere to most EU regulations. And the EU is absolutely attractive to its bigger economies, they get to pull from cheaper labor pools.