I think they want to get to raftel, I also think Gol D. Roger wasnt named the pirate king for being a pirate necesarily, but he found the true history and hid it with one piece. What leaves me to believe this is in skypiea, didnt what he wrote say something like "i left the true block(poneglyph) on that island"
I also think he turned himself in, but in doing so, he requested a public execution, during his execution, he told everyone about his treasure "one piece". So really his execution was to get his message out and get others to find the secrets he discovered. He probobly did this due to the extent the WG would have gone to contain this knowledge, they destroyed an island, so if he published his discoveries, they would be destroyed along with people, so he wants strong, detrmined people to share his discoveries with, and also doesnt want the WG to get its hands on it, so he hides it in Raftel, one piece is not a treasure, but something to do with th civilization.
this brings me to why the WG wants to get pluton. No one so far has gotten to raftel except for Gol D. Roger. no one in the WG is powerful enough, so they want pluton to go to raftel and destroy "one piece" once and for all, if they do, the 100 blank years will be erased totally and their secret will be safe.
The other way to keep their secret safe is by killing Robin, she is the only person who will ever be able to read poneglyphs(if she dies before teaching it), so if they kill her, even if you get to the rio poneglyph, its meaningless. So the WG doesnt want nico robin to resurrect the weapon, they just use that as an excuse to arrest her(the cant say, we want her dead cause she can find out our secret) but they are telling the truth, she can ressurect the weapon pluton, its in raftel. Gol D. Roger used pluton to get there in the first place. Tom built it for him. Gol D. Roger requested it to get there for all the stuff above. Tom trusted him, because he was, well, like luffy, in th way he asked him and spoke of his dream, the dream is a little to early to say(probobly protect this worlds history), tom possibly created pluton, but its a little early to say.(those blueprints looke very new, and were signed by tom, right?) ancient deadly weapon was probobly a lie started by the WG(I know im talking about conspiracies, but take robin for example, they said she destroyed 7 marine warships, they lie alot when it comes to the poneglyphs)
The ship was probobly known as super dangerous, when it was able to get to raftel. and before you say it was named something else(I forget the name) Gol probobly pulled a luffy and said" Pluton?, I dont like it, Ill call it …...."
So anyways, these are a bunch of thing I was thinking about during math class(boring as hell),