Without wishing to stick my head too far above the parapet, this has been going on for longer than the current crop of students have been alive. So any criticism of their actions should be a criticism of their culture. A lot of the commentators have been going on about "privilege" as if this means anything - in my view it's a bit of a red herring.
What these kids are trying to do is being transgressive, and dunedin around undie 500 time is probably their big opportunity - maybe their first and maybe their only real chance, so they leap at it. Dunedin really feels like it is so far away from anything, it attracts a large population of people who are seeking something different or extreme - if they didn't they'd stay at home in auckland or christchurch and live with the folks while they studied.
as someone, or anyone who was there in 88, or 90, or 93 would recall, the police in dunedin appear to deliberately ratchet up the tension (with riot gear, or barking dogs) in order to frighten the students (who it should be remembered include out of towners and high school students) into dispersing peacefully - and time after time this tactic is shown to be a miserable failure. It actually gives more emphasis to the transgression, which of course is happening well away from mum and dad's concerned gaze. A lot of this is simply acting out, nobody could imagine a return to the real bad old days, say before the hostels were "cleared" of returning students in 1989, but a lot of people would love to emulate the experience of those days. And they just have, courtesy of the police.
My money (50 cents down) says we'll have the same conversations in 10 or 20 years time. Maybe they'll even reprint "ritual song of defiance" so people can get some perspective?