Within the university system we have three main academic groups: undergraduates, graduate students (not "graduates", oh no, although "grads" or "grad students" are used), and professors/doctors. It's pretty easy to assess the first and third of these. Undergraduates are solely students; professors are teachers and researchers. Undergraduates have little to no academic authority; professors have a great deal of authority within their field. Undergraduates receive guidance and instruction; professors give it. Undergraduates are usually called by their first names, while professors are usually called by their titles plus their last names.
The graduate students are in the middle of the bridge. They are still students, but they are also graders or lecturers or teaching assistants. They fill in the age gap (22-32, let's approximate) between undergraduates and professors pretty neatly as well. They have a strange amount of authority, in transition from one academic class to another. They are not just allowed but encouraged to call their profs and advisors -- people with doctorates, who are officially on a higher intellectual level -- by first names. They have to decide what their own students should call them. People who have hardly even been addressed as Miss X or Mr. Y, being too young previously, are suddenly getting student papers in which they are listed as "Doctor X" in the MLA heading, getting sample textbooks addressed to "Professor Y".
It's a very strange sensation to be given a title of such heavy intellectual authority when you know you have not yet earned this title. You are a member of your academic department, but not a professor, not really a full member. At the same time, your students are obviously seeing you as an intellectual authority, which is good -- you are their teacher, after all, and you do have some authority over them. But this kind of thing makes it difficult for graduate students to place themselves accurately within the university's social and political hierarchy. You do not have full authority; you do not have zero authority. Where do you go?
You can go the first name route. You identify with your students. You were one of them not too long ago yourself. Some of them may even be older than you (yes, that happened. It bit, thank you). Hmm, hold on. On second thought, the first name is a little casual. Yeah, you are used to being called that. It feels normal. It does not feel unnatural to introduce yourself by your first name on the first day of class. You feel like yourself; you are comfortable with yourself, and you need to be as comfortable as possible in front of twenty thirty forty pairs of eyes. Then again, they are critical eyes. What if your students identify with you too much? What if they start to consider you just another person in the class? What if you do not embody the authority which you hold? You know they must bitch about you outside of class; you've done it yourself for your entire academic life. What if they start to hold you in contempt?
Yeah, maybe it's better to call yourself Ms. X or Mr. Y. The title will help you keep your distance. It will establish you on a higher plane. It will give you the authority you aren't quite sure you deserve. But you're in graduate school, after all. The admission committee thought you were good enough, and here you are, teaching, and so they must think you deserve your doctorate, and you desperately want it, you would do anything for it. That piece of paper, that title added to your name, to your identity, to you. You will eventually be a full academic authority. You will be a professor. So if you deserve your doctorate, shouldn't you also deserve your plain adult title?
It's not that it isn't your title; no one would dispute your right to call yourself Ms. X or Mr. Y. It's just that you are on a strange level. You ARE still a student. You ARE barely out of undergrad. And the only place you've ever been called by your adult title, besides in the DMV line, is on the birthday card you get from your grandparents every year. How old are you? I am 24. But how old is 24? Numbers don't matter; intellectual authority matters. Where do you fit in the hierarchy? Where do you fit within your academic society?