Like a lot of seagoing stories, "MS. Found in a Bottle" focuses on the great unknown, and what happens when someone boldly goes where no one has gone before. Granted, in this case it leads to a lot of variations of "we're all going to die!" but the principle is sound. The narrator journeys to waters where no ship has ever sailed before, and discovers new things about the world… specifically a giant whirlpool at the South Pole. One could argue that the story is a cautionary tale, since we'd bet any money the narrator's not chilling in Atlantis with a mai tai in his hand. But hey, you could also argue that the story stresses the wonders of discovery, and argues that even death may be worth it to see someone new and extraordinary.
Poe's not a huge fan of exploration here. In fact, this seems more like a cautionary tale, where he's highlighting the fact that for every hero of discovery, there's some poor sod that winds up at the bottom of a whirlpool with a bunch of dead guys.
The whole point here is that danger is worthwhile if it means seeing incredible new corners of the world. Who cares if you wind up in a whirlpool at the end of the day?