It's certainly not uncommon for celebrities to take up political causes, though this does not usually lead to them getting arrested for holing up in a high tower oil-drilling ship for four days. What's less common is for this interest to burgeon into a full-on obsession with all things philosophical, but that's exactly what happened to Lucy Lawless (best known as Xena, the Warrior Princess).
"I went to the UN summit on sustainable development after getting involved in the whole... big oil protest... and I saw all of these people working very hard but seemingly at cross-purposes about how do we create a just society." On a full two-hour episode of The Partially Examined Life Philosophy Podcast (which she claims was largely responsible for turning her on to philosophy), she describes how this political interest drove her to look at the foundations and histories of theories of justice, and eventually decide to go back to school to study philosophy, which she's now doing in New Zealand between flights to the states to film TV spots such as her recent appearance on NBC's Parks and Recreation.
The Partially Examined Life interview with Lawless is a five-person, roundtable discussion of Tom Payne's 2010 book, Fame: What the Classics Tell Us About Our Cult of Celebrity. You can listen here:
The thesis of the book is that celebrities serve as an outlet for society's aggressive instincts. Drawing on canonical texts about religious anthropology like James Frazer's The Golden Bough, the author compares the treatment of modern celebrities to ancient rites where young maidens were lavishly bestowed with fineries and then sacrified. Lucy thinks this well matches her own experiences, and talks about the existential weirdness involved with being and dealing with the famous.
Mark Linsenmayer runs the Partially Examined Life philosophy podcast and blog.