@Rotten:
I can tell that you watched the anime to catch up with the story as opposed to reading the manga.
16characters of nah.
@Yosemite:
Well I feel like the answer to both your questions lies in one time where Luffy said that "The Pirate King is the most free man in the world." I believe in One Piece, a pirate is someone that takes it upon themselves to be free, to combat any kind of oppression that they feel for the goal of sailing the world in lawlessness. And what makes Luffy's pirate crew is the sheer fact that they are free and combat oppression in any society they come across, including the World Government.
That's the thing, he could acheive the same by simply set sail, without ever being a "pirate". It's not like in OP world there are laws regarding entering a country territorial waters or anything like that. One can simply take a ship and travel freely through the world having adventures and meeting people, there is no need to call himself a pirate.
If Luffy never said he was a pirate and decided he was just a guy traveling to know the world, he would have all the adventures he had, would do all the things he did, but would not be seen as a criminal and persecuted by the WG.
He wanted to be a pirate 'cause a pirate is free, but it seems being a pirate only meant he lost some freedom to do what he otherwise would be able to do more freely.
Sure, eventually he would be deemed a criminal anyways when he turned against the WG in Ennies Lobby, but still. Just rambling though…