TheCSO points out that using "Philistine" as an insult is technically an ethnic slur, it's just a slur against an ethnicity that has not existed in a long time.
As pretentious as I'm sometimes accused of being, I will confess that I don't really run around calling people "Philistines" much. As a term, it's a little "Look at me, I'm a bohemian with an expensive education" for my taste though I am sure it has its moments.
But since the whole "The Cubans CC knew growing up use 'boat people' non-pejoratively for people who took a self-help approach to get to America, but the Vietnamese consider it an extremely nasty ethnic slur and she will get yelled at if she uses it on her blog the way she always heard it used"* fiasco of '06, I generally assume that if I even have an inkling something could be construed as insulting to an ethnic background, I should never ever use it.
At the same time, there aren't any actual Philistines left to offend.
*For the record, the context was that anybody who had the brains and gimp to build a boat and sail hundreds of miles to get here deserved to be an American and probably had awesome genes our culture needs.