Just before I get on to my theory here, I'd like to point out with the revealation of Gear 3, Luffy very well could be descended from Giants. That would explain why his arms and legs get so abnormally large when he's doing Gear 3!
I think it's more along the lines of "balloon" physics - the actual size of a deflated balloon isn't nearly as big as the actual size of an inflated balloon, so his skin and bones are probably just stretching, just like he does for his balloon move.
Anyway, for my theory, traces all the way back to not just Robin's past but also draws in Nami's, Sanji's, and possible Zoro's past as well!
If we look at the WG as doing all of this stuff to hide the True History, then what else could they have done? We have yet to learn of Sanji, Nami or Zoro's true homes so maybe they left home because something like Ohara happened there.
Dude, I'm so glad I'm not the only person who thinks about this! It drives me nuts that we have so little information on Zoro and Sanji's biological family and homes, Sanji's in particular because he ended up in a completely different part of the world from where he was born (though it's not disclosed exactly where Zeff attacked the Orbit.)
Nami's past I'm not as optimistic about because of how young she was when Bellemere adopted her - there's no way a relative would recognize her or she'd recognize them unless Oda did something corny like a family birthmark or a long-lost twin sister (and although a twin would bring about some priceless confusion gags amongst the crew and Sanji's head would explode from happiness, I hope that doesn't happen). Besides, she would still consider Nojiko her sister and Bellemere her mother.
You can also probably add Franky to the list of "Straw Hats/Potential Straw Hats With Mysterious Pasts" because he stated in a flashback he had been abandoned.
This theory only really works for Zoro and Sanji. Nami was found by Belle-mere on a ravished island 15 years ago…..but what was Belle-Mere again? A marine! So, is it not possible that the WG attacked Nami's home island in search of the ancient weapons or for another reason like Ohara?
There's so little we know about the attack on Nami's island of origin - the manga is very vague, only that Bellemere was dying and Nami was too little to know what was going on around her. We don't even know where it was (for all we know it happened in South Blue, the only ocean the SHs don't have a member originating from that we know about).
And Bellemere found them closer to 17 years ago, but the math doesn't hurt the theory
Following this, it could explain Sanji's past only showing him on a boat before Zeff. It means something similar could've happened when he was younger and he went with some refugees and became a chef….or he was a chef before.
Or why Zoro was just a student in the dojo and we don't know anything about his past beforehand, either. I think the anime showed that he was a wandering toddler until Kuina kicked his ass, but it's not manga canon and if something happened later on, well, it wouldn't be the first time the anime screwed with manga canon, anyways. (Zoro: Yay, I can cut steel before we enter the Grand Line! Chopper: Yay, I can eat Rumble Balls like potato chips as long as I'm in a Davy Back Fight!).
The other thing that kind of bugs me a little about Zoro and Sanji is that despite being normal humans, they're both absurdly strong without the assistance of a Devil Fruit - granted this is fiction and more importantly a shonen manga, but most of the really strong opponents have had a Devil Fruit or some really strong weapon. Kuro is the only one off the top of my head who didn't eat a DF but was still able to do something next to physically impossible, so I'm very interested in seeing the family trees of those two.
This theory becomes more sound with another theory mentioned earlier on. Someone else has said that maybe all the islands of the world could've been connected until the weapons were released. So maybe all of the world's islands were once a part of this giant civilaztion. That, or like another theory, all of the Grand Line was.
Ignoring the giant weapon, that's actually how the continents in the real world were formed - the 6 big land masses on Earth were once one really, really big land mass. It has a special name that I can't remember right now but I think it begins with "Pan-".
Anyway, this is not completely sound but it could work and it would explain quite a few things…..
Nah, I agree with a lot of what you said.