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.
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.