It's also much easier to defend in a "without rule of law" (WROL) situation. You've raised the bar for just getting to your place. Short of scuba gear, there's no way to approach a prepared island undetected. This even goes for the dark of night if the defenders are well prepared. Would be invaders would probably also be approaching without cover against rifle fire, unless they are hiding behind the engine block of a fairly large sized boat.

There are some disadvantages that come with that. A determined group could keep you trapped on your island more easily as well.

That's true on any large or remote piece of land, though, not specific to islands. It's one reason people who live in middle-of-nowhere Wyoming like it there.