Many a fan has imagined wearing a Starfleet costume. But we recognize it is a costume and not an actual recognized uniform. To wear one in the privacy of your own home and/or among like minded friends or at a convention is one thing. But to wear it in public as a substitute for everyday wear is something else entirely.
It's all very well to want to be ourself, but let's be perfectly candid here. In the real world if you wear such a costume in public for no reason other than as a substitute for normal everyday wear then you might as well also wear a big neon sign that says, "Please, beat me."