@Ubiq:
Why build a countermeasure if it's in the same category as the other mechanisms that nearly destroyed the world in ancient times?
Very easy, the Ancient Weapons are the ultimate power without anything superior to them (it seems so at least to this point). So since it is the non-plus-ultra you can´t build anything superior then that. So the only logic countermeasurement is to have your own copy of the original. It´s the best thing to have don´t you think so?
They seem to reasonably sure that Pluton can be controlled by them.
Well they don´t have no other option. Iceburg said that Pluton was build by the ancient shipwrights of Water 7, so logically their only trump card is the blueprints of what they built. If they would have built the others too, then they would have passed on the blueprints of those aswell.
Plus we really don't know what was written about Pluton on the Alabastan Poneglyph though, whether it had been destructive or protective in nature.
Err, the nature of it doesn´t matter. The Poneglyphs tell the locations of the Ancient Weapons that´s all that matters. Here´s the part from chapter 218:
<<cobra: <em="">"There is no history of this country on that stone…!! It should have been everything about that "weapon" you wanted...!! …and its LOCATION...
If you had told Crocodile that…In that instant this country would have been his. Am I wrong?"
You see, just as Poseidon the original Ancient Weapon Pluton exists and the Poneglyph tells its location.
The blueprints are really just there to build your own copy if things go wrong. I know you don´t like the nuke analogy but I think it still explains it best. Nuke´s are still the ultimate weapon in the real world. And what are the countermeasurements against them? That´s right nukes. Of course having a nuke of your own doesn´t protect you from the effects of one that hits you, but showing your enemy that you have one and that you are willing to use it against him will make him think twice if he really wants to use it against you and vice versa. That´s how the Cold War has worked over decades. Of course we know that if either side would have attacked, there wouldn´t have been a winner. But having no nuke´s while the other side has them is equal to suicide.
And in a same way I see blueprint Pluton as a countermeasurement to original Pluton, Poseidon or whatsoever. It is neither superior nor inferior to the other one, but having none at all is a direct suicide.
As I recall, that they were two different things was something that I picked up from ocean, might have been a misinterpretation of what he meant though.
Not sure what you´re talking about, but if I guess correctly then it is Robins statement that there´s two kinds of Poneglyphs. Stones that contain information and stones that lead to these stones (in other words a guide). And she says that the Poseidon Poneglyph is such a stone that contains information, which means that the Pluton Poneglyph must be the same.
Well that´s the only thing I could think of about the two different things statement. Is that what you meant?
Many of the places that encountered the Ancient Weapons are mere shadows of their former selves, the High Jayan civilization is gone and only the Shandorans remain. Water 7, on the other hand, seems to have maintained itself in a way. They were shipwrights then and shipwrights they remain. They must have had an ace in the hole.
Huh, wasn´t Water 7 going down in more then one way before Puffing Tom was built? The city got what it is today thanks to the Seatrain. Before that the people of Water 7 lived a rotten life full. The remaining Shandorans actually lived better then these until they got sent to Jaya.
And the old city of Water 7 is actually also in a worse shape then Shandora. Shandora remained a beautiful and untouched city until Enel came 6 years ago. The old city of Water 7 though sank into the sea long ago and the new city is built on its ruins. The ace in the hole that put Water 7 ouf of its misery was Tom-san himself and nothing else. And that´s an ace from recent history, not ancient history. 
</cobra:>
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