In the future, it seems, everyone will want to be the same. We saw this twice in Season 2. When we saw The Obsolete Man, the state wanted everyone to conform, to think alike. In Eye of the Beholder, everyone was supposed to look alike.
This time around, both things are true. Books have been outlawed because everyone is supposed to think alike, while everyone is supposed to look alike so that there is no need to discriminate or hate based on looks. Unfortunately it means that no one can tell anyone apart. Is that Uncle Rick, Doctor Rex or Psychiatrst Sig? In actuality, they are all actor Richard Long (from Person or Persons Unknown in Season 3), but the only other way to tell is to look at the name on the shirt.
And that’s just what Marilyn wants to avoid. Her father killed himself because he was so distraught about having undergone the transformation and now she doesn’t want to do so, but everyone wants her to pick the number of her perfect body. They won’t force her to choose, but they will figure out what’s wrong that she doesn’t want to choose. One day she wakes up and runs and runs until… she runs into the wrong room, and they think she’s decided to go ahead. So she comes out and she has transformed. Too late now.