@Ivotas:
Well for all we know at least Nico Robin must be convinced that it was the Buster Call that did it or else she wouldn´t be so affraid of it.
I must have missed this part, I don't remember anywhere being stated that the Buster Call wiped out any Island… what Nico Robin says about the BC is actually this:
<<robin: it="" is="" an="" emergency="" summoning<br="">of 5 Marine HQ vice-admirals and 10 battleships.
…nothing will remain of anyone targeted
by an international-level military force such as that.</robin:>
Now if this means that the BC fleet wiped out an Island, it would imply that ALL people in the island were targeted by the BC fleet.
Let's gather some facts: Iceburg says that Nico Robin is the only person in the world that can decypher the poneglyphs. We know that Nico Robin is terrified about the BC, and of Ao Kiji. We also know that Nico Robin held the same dangerous opinions as the Demons of Ohara even as a child, 20 years ago. I think Ao kiji also mentions that Nico Robin escaped once from him. We also know that Iceburg thinks that the pursuit of the knowledge of the poneglyphs, even if not linked to the reviving of the ancient weapons, is very dangerous to the world and could lead to its destruction.
Now this is how I see it: The demons of ohara, as Iceburg refers to them, are a group of people whose desire is to discover the true history, which is why Iceburg says that thing about the dangerous opinions. (Notice that the only thing robin says is "what do you know about ohara", not referring to them as "demons") Apparently, the WG thinks so too, because these people refuse to quit their pursuit of the true history. It seems unlikely that a whole Island is involved in such a delicate matter, let alone say that all the ppl in the Island can read the poneglyphs… it just seems like too much ppl, but let's not rule it out. So the WG summons a Buster Call, with Ao Kiji as a vice-admiral 20 years ago. The BC, especially Ao Kiji destroys the DEmons of ohara, Ao Kiji captures NIco Robin because he is unable to kill an 8-year-old (I think Ao Kiji is one of the Good Marines), Nico escapes, she gets the bounty and the rest is history.
EIDT: One more argument for this is the discussion that Spandam had with the Gorousei:
< <gorousei: so="" it="" did="" exist,="" after="" all.<br="">< <spandam:this is="" no="" time="" to="" be="" discussing="" preventing="" the="" resurrection="" of="" ancient="" weapons!!<br="">If we are to maintain order, we must arm ourselves accordingly!!! WE MUST TAKE THE ANCIENT WEAPONS OURSELVES,
AND STRIKE THIS AGE OF PIRATES FROM OUR HISTORY!!!!
< <gorousei: the="" times="" are="" changing.="" he="" is="" not="" without="" a="" point…<br="">Then seize these "blueprints" first.
We will discuss from there.</gorousei:></spandam:this></gorousei:>
This seems to me that the WG shifted their opinions: first they tried prevent any resurrection of the ancient weapons by annihilating the ohara demons 20 years ago, but 10 years later after having lost trace of nico robin and seeing how the pirate age is in full bloom, they decide to go for the blueprints.
Anyway, its all just a theory, i really get your point Ivotas with the "Demons" being the BC, and its possible, I just think there are other hints that I interpreted into this whole thing… might be all wrong though
There's one thing I didn't consider because i don't have the info, but maybe someone knows how old ao kiji is? I mean, 20 years ago he might have been too young to be a HQ vice-admiral?