The Americans only English society's decisions to say "zee" instead of "zed" is truly astounding. Why would Americans insist on saying "zee" when the correct pronunciation is so clearly "zed?" In time, the only way such incredible inconsistencies will be remedied is if Americans adopt the international English conventions, and that is why they eventually will.
Americans will not adopt to international English conventions. There are many words that are pronounced and spelled in a distinctly American way. These including saying "zee" instead of "zed." There are many other words, such as labor, that have been spelled that way for a long time. Americans have shown no desire to change the spelling or pronunciation of these words.
No, Americans will prove as stubborn in its resistance to "zed" as it is to the metric system. It does not matter that changing would prevent the numerous mistakes caused by confusing C with Z; this is the way Americans have learned it, and so it shall remain. Call it an extension of American exceptionalism if you will.
There are a lot of small differences between American and British English, and neither group has any need to switch over to the other norms. These differences are cultural and deeply ingrained, and if they ever did change it would likely take generations and increased immigration and globilization to mix the cultures.
There is nothing wrong with being different. We will never stop being our unique selves. We will never change who we are.