My friends had answers ready for me as well, including: nostalgia - they wouldn't want to adulterate their hallowed undergraduate experience with murky twilight memories from their graduate years, wanderlust - spending another four or five years in the same place would be terribly parochial, and of course, stigma. It's not that the stigma held by undergrads against grads isn't ubiquitous across all college campuses; it's just that at Princeton, it's unusually strong.
As it turns out though, none of these arguments really holds water - but like me a year ago, my classmates had not bothered to take a step back and redefine how they saw Princeton differently after graduation, and so still held the same opinions of Princeton that they had built during their undergraduate years or even in high school. But why bother to form a new perspective? Why change what and how we think of the University when we all had such a great experience as undergrads? One simple answer overwhelms - not surprisingly, a university isn't just for undergraduates, and has more to offer, like faculty contacts, seminars, vocational programs, jobs ... oh yeah, and grad school.
So I would like to expound upon the differences between graduate and undergraduate student life, and discuss why the uniformed opinions we hold as undergrads could serve to both our own and the university's detriment.
One reason that graduate students live different lives than undergrads is obvious: We don't want to be undergrads. We were undergrads once - and then we graduated. Undergrads and recently graduated alumni often don't consider that grads might have developed this alternative perspective. Though graduate students still like to go out and be social, graduate school is more like a job - we conduct our own work, we're paid to be here, we have a boss and an office - and we maintain a degree of separation between our jobs and our lives instead of living within the immersion environment inherent in the American undergraduate educational system.
For example: graduate students rarely visit the only real outlets for nightlife in Princeton - the eating clubs - not because we can't get in (trust me, we can and sometimes do), but because we no longer have a strong desire to stay out late on a weekday talking campus politics with people four years our junior. We would like to have interesting and engaged conversations with undergrads, just not while throwing elbows waiting for a beer in a dark basement at 3 a.m. Analogously, from my experience, going to the Street now is a lot like an undergraduate going home for Fall Break and showing up at a high school party - fun for a while maybe, but not something you want to keep doing.
Correspondingly, when I came back to Princeton I didn't miss the Street or my old club (Cottage), and my undergraduate memories weren't tainted - I just saw it as the place where undergrads go to hang out, and where I might have a meal from time to time. I didn't walk across campus reflecting upon how boring and detached my life had become, but instead was excited at the prospect of meeting new people in interesting fields of research. Of course I remember how great Princeton was as an undergrad, but looking around after graduating and working for two years in New York, N.Y., I see the campus in a new light, with a great many new opportunities revealed.
Why then, are we as undergraduates so averse to the idea of coming back? In part, it's because we've completed one aspect of our lives and compartmentalized it in our memory. We're linear-minded, driven Princetonians, and we want to move forward, not redefine the past. But it's also because the majority of undergraduates on campus have almost no contact with the graduate student - or at least they didn't when I was an undergraduate, before the advent of four-year colleges - and this obfuscates the view of Princeton as a true research university as opposed to a solely undergraduate college. We do not interact with and therefore cannot relate to graduate students, and though this often leads to good-natured joking about the graduate side of the university, it also means that undergraduates lack the perspective and role models crucial to forging an academic future.
As a returning student, I realize that a Princeton graduate experience is very different from a Princeton undergraduate experience, though as undergrads I believe we tend to forget why it should be. I lacked the perspective to realize when I was an undergraduate, in large part because I had little to no contact with graduate students. I feel strongly that encouraging informal interaction between grads and undergrads, say, perhaps, by promoting joint events - all students love free food - moving more graduate housing onto campus, or hosting some graduate events on-campus as opposed to at the grad college, would help bridge this gap. These types of events certainly would have helped me as an undergrad, and perhaps saved my old classmates from hearing a lot of defensive explanation.