Though Netflix's live action One Piece's success has probably been driven by it's long-time fans, as someone who isn't familiar with One Piece, I approached the show out of sheer curiosity, only to be delighted at the dark thread the story held, especially when it came to the theme of following your dreams.
It's no surprise to those who are familiar with One Piece that the show isn't for kids. It certainly features a dark undercurrent, with suitably unhinged villains and a fair amount of violence. But what surprised me about the show was the underlying thread of darkness around Luffy, the show's perpetually optimistic (and joyously likeable) protagonist.
Now optimism is a complicated character trait to broach in fiction, as it can feel overwhelmingly one note. What makes Luffy's optimism interesting is that his optimism also holds space for danger. This comes across most clearly towards the end of the season [spoiler warning] when Luffy's first mate Zoro challenges the world's best swordsman to a duel.
Though the crew's navigator Nami immediately tasks Luffy with convincing Zoro to back out of the fight, Luffy refuses. And Zoro is beaten quite badly and left on the verge of death. The nuance here between Luffy and your run-of-the-mill optimistic character is that even after he realizes that Zoro might die, Luffy still refuses to say that he would have stood in between Zoro and his dream of becoming the best swordsman in the world. Not because he doesn't realize the danger - he does very clearly now, but because, to him, following your dreams is essential.
Throughout the season, Luffy asks each person he comes across a question that no one else will ask these characters - what do they really want to do with their lives? And in doing this, he frees them. Sometimes he literally frees them from their circumstances, as in the case of Koby and Nami, but mostly, he frees them from the framework that the world has built for them. His belief in them and their own ideals gives them space to believe in a different world for themselves. And sometimes, that's all it takes.
There are dangers that come with following dreams, but I don't think that the show is trying to say that following your dreams will always turn out well either. One Piece does showcase those dangers, but on the other hand, it also shows the dangers of what happens when you don't follow your dreams too. And over the course of its first season, One Piece lets that question play out for the audience, leaving it up for them to decide.