Let's all take a deep breath. Okay? Okay.
Now let's take a look at why certain parts of the lyrics do not fit the theme of One Piece.
"Look, there you are my love, waiting in front of me."
This is my biggest gripe. Not one month ago, Oda was quoted in Shonen Jump magazine saying, in response to a question as to who in the crew "Nami likes", that there is no romance in One Piece. Therefore, in One Piece-verse, there cannot be a "love, waiting in front of me." Take this any way you like, but when it's used in such instances as scanning over the crew's faces, or Luffy falling towards Ace, it really comes across as being very very much out of place.
Now let's take a look at why the mood of the song does not fit the mood of One Piece.
The first half of the song, it can be argued, fits all right with the animation being shown. Happy lyrics, happy scenes. However, when the animation switches to scenes from Impel Down and Marineford, the tone of the song seems very much at odds with what is being shown (except for the one notable exception of "Fuu fuu yay"). Perhaps the directors behind this opening merely wanted to offset the horrible torture and carnage of these two story arcs, but a happy sounding song simply does not fit.
I'm not arguing that the two halves of the opening animation are irreconcilable, or that a song on the opposite end of the mood spectrum would fit any better. I would even admit that the lyrics could, with very little tweaking, be made to fit the mood. What I'm arguing is that the tone of the song needs to be changed so as to attain a better balance between the happy and dark sides of One Piece. Yes, this is a kids' show, but it is a kids' show with fighting, death, and all manner of darker themes, and the current opening song is doing nothing to acknowledge this side of it.