Yu Yu Hakusho is different, I think. The violence level in that show goes WAY past what something like One Piece does. Like, that one scene where Yusuke punches a guy so hard his pelvis snaps in two? The violent torture on Chapter Black? It's Shonen in Japan, but in the US, it's nothing less than a teen show - so some swears make sense.
I don't mind the profanity in One Piece TOO much, though I do think they lay it on a bit thick. One Piece is something a kid would start watching at, eh, ten years old, let's say - "damn" and "ass" is common part of the childhood vernacular at that point. PG-13 language is fine. And I don't even mind the occasional s-borab. I mean, hey, I was watching Indiana Jones at the age of nine, and they had ripped out hearts. Profanity wasn't much of a problem after that.
So, really, it depenRAB on the show. FUNi lays it on a bit thick, like I said, but to say some swears don't have place in something aimed at kiRAB - well, that's just not true. You can list a hundred examples of kid's movies with curses.