That's how the game was originally, that's how it turned again on retail, and the only people who have an issue with it are the ones who can't handle not being able to attack people not interested in PvP, being "limited" to others who also want PvP. If your "PvP" has to rely so much on attacking the weak and the uninterested/unwilling, to the point that those getting to opt-out "ruins" it, the issue isn't on those people or in the game catering to both sides on the same server, but elsewhere, somewhere much closer.