I suppose class and Social Security are actually much the same. They're the "third rail" because the former freaks out elites and the latter angers them. The country loves Social Security and probably could handle a conversation about class if the Villagers didn't nuke any candidate who dared bring it up.
It's actually kind of funny thinking about how for so many years I'd internalized this notion of Social Security as the "third rail." You know, it's so dangerous that only really brave politicians would mess with it. Of course it's incredibly popular because it's a great program, people like it, and there's no reason to mess with it. But we've had decades of elites and the "pain caucus" and other wankerific manifestations of people who really can't stand the idea that old people get a modest guaranteed income after paying into an insurance system their whole lives.