Well, I start out with this in all seriousness, but I think if we expand on it, adding clauses to explain oddities in the OP world, it could also rapidly become hilarious.
We know the WG is desperate to keep the True History (as recorded in the Poneglyphs) silent. The theory has already been floated it's because the leading nations of the WG don't look too good, and may in fact be fingered for a terrible disaster (possibly to do with the Ancient Weapons).
My theory:
The nations leading the WG actually were the agressors in a war with massive social and ecological costs. The result is that the OP world of the 'present' has a few remaining patches of 'ancient' more advanced technologies which were abandoned or rendered worthless in the war. This is why everyone has sailboats AND Franky can have a fridge in his torso. Most of the new technologies were lost, but there are enough bits and pieces to cobble amazing things together left.
The war also had such a monumental damage to the ecology as to inspire great mutations. The fishmen? The Devil Fruit trees? Mutants. Sanji's 5 percent mutant, explaining that eyebrow.
As said above, if these facts came out, it looks very bad for the powers that be, hence the forbidden nature of the Ponegyphs. This also likely got reinforced over the years, because the ancient technologies, if recovered, could rock the boat of power. Commerce would be reinvented if modern shipping boats came into play. Wide access to information would benefit populist movements by letting everyone see governmental incompetence live.
What am I missing?
