'I want everyone to be a pirate' is actually likely the dream the more I sit on it
Obviously not my original idea and has been kicking around the fandom for quite some time but the more I think about what boxes the dream needs to tick to fit the more this one just seems like the natural conclusion
Lets quickly breakdown the criteria
Has to be something a child could think of
has to sound ridiculous and nearly impossible
needs the authority/prestige of being Pirate King to accomplish
Needs to be something Roger would also want to do
We don't know all of Roger's life and ideas but we know he was similar to Luffy, and we also know while terminally ill he decided to give himself up to intentionally spur on a new generation of pirates
This act created the pirate era we know today and while he didn't accomplish turning the whole world into pirates he absolutely intended to create a burst of ambitious people turning into pirates as his final act before death
Like Roger as PK telling the world to go find his treasure Luffy recognizes that being the PK is a huge step in influencing the world and changing it which makes sense why he feels he needs to be PK to accomplish this.
It's also a dream that ties into the major conflicts in the story, for Luffy to accomplish this he needs to tear down the current system with the Celestial Dragons
Considering Luffys love and obsession with pirates as a kid it makes perfect sense for young Luffy to dream that everyone could be like that
I don't really have much more to say, it's ridiculous, it's something Roger attempted to do in his life, it's something Luffy needs to be PK to do, and its something that organically gives him a reason to topple the World Government