While I am part of the 'zed' group, there is no "correct" pronounciation for anything because it all depends on accent and culture. Just embrace the diversity.
The reality is that American english pronunciation of "Zee" is globally more popular than british english "Zed". As a descriptivist for linguistics, I believe language IS how it's used, not how it ought to be used. So I was being over-the-top calling "Zed" a mispronunciation. But it's just as, if not more, wrong to call "Zee" the mispronunciation too.