Strategic default

I bought a house in Southern California a few years ago, meaning I now owe more than my home could be sold for. Despite not having bought a house as an investment, this situation is not a financially strong one. I've heard about people walking away for some time, even heard of people who insist it's the only reasonable thing to do but now those voices are getting more mainstream. Greater financial powers are running a huge guilt trip in response but their own hypocrisy makes that difficult to hear. Many good writers are making good arguments, so why do I keep paying my mortgage?