Look. It is true that many people in early /a/ were One Piece fans. But it's also true that early /a/ had plenty of Naruto fans. Saying that all veter/a/ns are One Piece fans or vice versa is highly erroneous. Especially considering /a/ has around 100 times the population it once had. The people calling others newfags? Probably just heard one bitter veter/a/n speak about it. Most of the people in this thread and the last probably don't even know why /a/ stopped talking about it. I'll give you a hint: It was long before the forced "Set fail" meme started.
tl;dr: Nowaday One Piece fans are crossing boundaries of faggotry they never crossed before, and it will come back to bite them.