This is a far too complicated topic for a short discussion. It has to do with people's origins and reasons for joining, less so based on their experiences. And cultures like that tend to self-reinforce to a certain extent. One interesting thing I've noticed among officers is that the more conservative officers tend to be more willing to bring up politics, because they assume everyone else will agree - even though that's rarely true.
If you really want to dig into the topic, I'd recommend this book. Matti's helped write it.