At least at the "top" programs (don't start arguing about what that means!), there's almost certainly no conspiracy or evilness in the question. It's just a question like any other to try to get to know you. If the program is interviewing you, by definition they are interested in you. If you answered with programs they consider "lesser", they'll feel good they have a shot at getting you (they will NOT think they made a mistake in interviewing you based on the other places that gave you interviews, because "top" programs don't make mistakes 😉 ) And, if you applied to other "top" programs, they'll still think they have a shot at getting you because they'll think you'll realize that their program is the best. So, I really, truly, honestly don't believe that answering the question hurts an interviewee at a "top" program. If anything, it could only help (if the program recognizes other programs that they see themselves competing with, they might recognize it will take more than the average effort to convince you their program is best).
And, at "not-top" programs it still won't hurt you. Even though they may recognize that you have applied to more prestigious programs, they won't rank you lower and they won't suddenly decide they don't want you. If anything, applying to "better" programs is more likely to enhance your status because, after all, you are interviewing with them and they will interpret that as interest on your part despite the other programs you applied to.
It's mostly just a question with no evil intent. I would be annoyed if it were a question that led off the interview (because it's not that important a question in getting to know you), or if an unskilled interviewer started focusing on your other choices too much. But, the question itself is not meant to make you uncomfortable so being evasive or coy is probably more telling than a simple honest response.