We all know our favorite pirate, Monkey D. Luffy, who is well known for his rubber powers and straw hat, but what if Luffy wasn't a pirate. What if Luffy had never met Shanks and instead listened to Garp?

Luffy
Luffy is the fearless captain of the Straw Hat Pirates. He knows when to retreat and also when to stay and fight, but he may have been different if he was a Marine instead. Luffy only became a pirate because of Shanks and he now has to fulfill his promise of returning Shank's hat once he's become a great pirate. If Luffy hadn't met Shanks, he would've only had Gary's influence to grow up with, most likely turning him into a Marine.

The Crew
Now if Luffy was a Marine captain, he wouldn't be gathering a crew to travel across the ocean. …show more content…
He only joined Luffy because the restaurant basically kicked him out and forced him to join the Straw Hats, but Luffy, being a Marine, would already have a chef, so Sanji wouldn't join.

Chopper isn't even worth discussing. Chopper is similar to Sanji, where Luffy would already have a doctor and would have no need to visit Drum Island.

[I]Robin was literally just a criminal her entire life known as "Demon Child Robin." I can't see her joining the Marines, her enemy.

Franky would also have no reason to join the crew if we're being clear here. Same with Brook. Like I'm not even going to go into why with these two. There's just no reason for them to join him if he's a Marine.

Straw Hat Crew's Fate
So in the end, if none of the Straw Hats had joined Luffy, their lives would be shit. Zoro would've been executed my Morgan, Nami would've remained a slave of Arlong until the day she died, Usopp would've just stayed on his little island, Sanji would work in the sea restaurant forever, Chopper would've wasted his life at Drum Island, Robin would forever be running from the government, Franky would just be chilling at water 7, and Brook would be left to wander the oceans for all eternity without a shadow. It's kind of sad to think about how much Luffy has changed their lives throughout the Manga /