I've always felt like it should be optional. LFD and LFR are optional ways to group with a larger pool of players from beyond your own realm, and CRZs are effectively the same thing for open-world play. Yet, for some unfathomable reason, they're treated as a baseline part of the game rather than a feature you can toggle on or off. There's no other area of the game that's had the option to only group with players from your realm removed from it. We can form raids, queue for dungeons, and organise BGs on our own terms. But for some reason we can't play in zones that aren't full of people from other realms.
And it's almost certainly not to do with the technical issues of creating an opt-out switch -- players were able to block their client from being CRZd from the start by using various bits of software to prevent connections to other servers. If players can manage to escape CRZs on their end with a few minutes of work, I'm pretty sure it's not an unreasonable request for Blizzard to implement an option in the UI that does the same thing.
I think the CRZ technology is awesome, and it's a great feature for WoW to have -- provided it's a feature. Right now it's not a feature, it's the way you have to play the game whether you like it or not.
Options are a good thing.