People seem to be taking this "force of nature" a little too to the letter.
"Force of nature" is more… a brief summary of what Logia abilities entail...and then abridged from there.
I know I'm repeating myself, but let's review.
http://www.mangareader.net/103-2648-10/one-piece/chapter-541.html
Here we see Crocodile's ability summarized as:
A sandman, Crocodile is able to manipulate sand and turn his body into it.
So attributes of Logia include: 1) Ability to manipulate one material, substance, or element. 2) Turn one's body into that same material.
You don't have to read too far to see the third attribute.
I choose this one. http://www.mangareader.net/103-2654-7/one-piece/chapter-547.html
Other examples exist, but here is clear that Logias can 3) create the same material point 1 and 2 differ to.
Other attributes given to Logias, such as phasing attacks through them, are just common associations. Crocodile and Ace could do this because they were made of sand and fire, respectively, but Blackbeard can not because he is darkness/gravity, which makes his Logia atypical from other Logias but still following the 3 rules of Logia.
Hell, if there were a fucking RICE Devil's fruit that followed these three rules, I'd back it as a Logia.
Points of debate:
Whitebeard: Whitebeard's fruit does not fulfill requirement 2. Therefore it is Paramecia.
Mr. 1: The Dice-Dice fruit encompasses his body, but does not extend beyond that. If he were a Blade-Logia, he could create and control blades over a large area. He is paramecia.
Caribou: He is capable of turning into swamp, extending the swamp beyond his physical boundary, and control the swamp he has created. He is Logia. Furthermore, though he is unfazed by attacks, they do not phase through him, but are absorbed into his body, which is unique to his Fruit, similarly to Blackbeard.
Any other disputes about these? I'd love to give it a go.