There’s a quote from Nichelle Nichols’ 1994 autobiography Beyond Uhura: Star Trek and Other Memories which pops up a lot in discussions about the TOS skirts:

In later years, especially as the women’s movement took hold in the seventies, people began to ask me about my costume. Some thought it “demeaning” for a woman in the command crew to be dressed so sexily. It always surprised me because I never saw it that way. After all, the show was created in the age of the miniskirt, and the crew women’s uniforms were very comfortable. Contrary to what many may think today, no one really saw it as demeaning back then. In fact, the miniskirt was a symbol of sexual liberation. More to the point, though, in the twenty-third century, you are respected for your abilities regardless of what you do or do not wear.