One of my own personal mountains to build is something better than self-interest to unite us.
I think that self interest can be uniting, if the correct conditions prevail that make one's self interest align with everybody's interest. For example, it's in my interest and everybody's interest for me to be healthy (and I suppose that's at least in part why you run to change the world, no?). This, obviously, is true for each individual, so why are we so unhealthy as a nation? Probably because the most immediate definition of 'self-interest' is economic/financial. Its too goddam cheap to buy a cheeseburger (for example a McDouble costs $1...One. Fucking. Dollar.). Helvetius wrote that through laws, men can be changed, and he meant changed, not just coaxed to behave better. I think farm, food, and health policy may be a clear example of his thinking, albeit in the opposite direction. We have perverted the incentives for people to derelict a lot of their own self-interest by passing laws that encourage a very few people to have a self-interest that does not intersect yours or mine (assuming you are not an exec at ADM!). And as a result the people are different, much different biologically, not simply behaviorally.
I have no idea how prevalent spousal abuse is. Far too prevalent, but certainly not anything like what is seen in countries whose laws don't discourage it. In Afghanistan, for instance, a girl can be forced to marry her rapist or else face the death penalty. I have never hit nor threatened any of the girlfriends I've had over the years. I like to think this is completely independent of the fact that such behavior is illegal, but I'm not convinced that such is the case. It seems where people can operate with impunity, they always do.
So my point is that we need good governance to ensure that all of our interests can align. I don't think this is overly idealist, nor do I think that it's unattainable. We are a better educated society than we ever have been, and we have far more access to information and debate than ever before (including forums such as this one). Right now, I think two of our biggest national nightmares are food policy and financial industry deregulation. These are huge problems, but the good news is that they're legislative in nature. They, therefore, can be solved. Mutual self-interest is supposed to be the whole point of capitalism. I think it works, so long as oversight is strong and education is ubiquitous.