A lot of things were being challenged in the 1950s, '60s and '70s. No matter how principled and moral something sounds in the real world you still have to deal with people's prejudices and preconceived ways of looking at things. From our contemporary perspective Uhura's role and Number One's don't seem like anything to talk about. Indeed Uhura isn't shown doing all that much (unfortunately), but her very presence was quite progressive for the time.
Very nicely put. It was AMAZING in 1966 to see people of color on American TV, who where not a maid....janitor...Pullman porter. Trek, I SPY, and M:I were IT. And the same for Asians who weren't running a laundry or a houseboy.