Most people who buy entire islands in Sweden are evil as in they are very very rich, don't give a crap about the local community, and do dumb things like build giant pools depleting the scarce local water supply.

But if you wanna start a cult just snag a big ole house in the relative boondocks and have it there. Creepy cults in the country are a staple of mid-budget TV action thrillers here, so apparently they're everywhere.