Dividing the officers -- in a very dressy, ornate and status-reinforcing style -- from the enlisted in their utilitarian one-piece, suggesting underclass status, was contrary to everything we have seen about Starfleet before and, really, since. Emphasizing class distinctions was very 1980s, but doesn't seem consonant with Federation or Starfleet ideals.
But it is very military. Like it or not, no matter what any script says, Starfleet is military. It has to be in order to function.
Imagine some new recruit, pissed at his superior for assigning ... I don't know, latrine duty ... saying "DUDE, NO WAY! I QUIT!"
Starfleet is not McDonald's.
Though, now that I think about it, McD's management does have a completely different uniform than line crew.
So, there you go.