It's one of those things that divides opinion. I remember Keegan being told off by Dave Wallace for saying Man City when he arrived as manager but, as you say, when I was a kid in the 70s I knew lots of people who talked of supporting 'Man City' and it wasn't seen as an issue by many of us at the time. Maybe 40+ years from now we'll all be talking about Citizens/Cityzens and saying it's not appropriate or something we use in every day speech while future generations may actually love it and use it all the time. There's probably someone somewhere who wishes we were still nicknamed 'The Cits'. These things come in and out of fashion (though I doubt Cits will ever come back).