If always enabled privacy is somewhat better, because it leaks less information about the user wallet software and user habits.
Notice how this tradeoff is fundamentally a political conflict between different classes of users: the tiny minority of centralized businesses(1) trying to accept zeroconf, and the much larger group of Bitcoin users who are harmed by the privacy leak of the opt-in flag. So it's entirely appropriate to treat this as a political decision, to be made by the wider community.
Of course, since zeroconf is so insecure, it'll only take a small minority of users/miners to render it useless with full-rbf... Kinda says something about how dumb this way of using Bitcoin is.
1) just two spoke up in favor of keeping zeroconf indefinitely on the bitcoin-dev mailing list.