Every so often, the idea that "we should change the world for the better" pops into someone's head. When this occurs, they -- like all thinking people that ponder over the deeper structure and meaning they see in this world -- sincerely wish for the world to become a better place.
After which, they go back to their lives. They go back to worrying about money or they go back to worrying about their future. They go back to worrying about their kids if they have any, and they certainly go back to worrying about their friends and family. They go back to eating, and sleeping; to reading, and to talking to people. They go back to following the world as it moves through its many various patterns.
Back to all of those things that bind us to our day-to-day existence. Some common things, some cultural and some regional ones.
In that instance, just before they turn back to focus on their own existence, they usually wonder: why is the world such a harsh place? Why do so many horrible things happen to people caused by other people? Why can't we fix things? Why?
And then they go back to their lives. Back to themselves, and away from all of the miseries that drag down humanity. Answering, by their very actions, the question that they just posed. For it is that we live in a harsh world because we choose to. Most people, most of the time, mostly prefer to direct their attention towards their own self interests. Of course, why would you not? It is after all, built into your very soul; possibly even your DNA. But it is that same evolutionary instinct for self survival that opens up the door for all of the world's horrible people to do their horrible things; all, of course, in the name of whatever poorly conceived justification they can conjure.
And so people follow, or they allow it, because at the end of the day they are just too tired from merely existing to be able to stand forth against the terrors unleashed or defend us from strife.
If it where, that the idea that "we should change the world for the better" would stay just a little longer in the minds and actions of more of the world's people, then we might reach civilization just in time to stave off our inevitable doom. Then again, grey might just be a better color for my SUV, it tends to hide the dirt a little better...