Chesterton does have a point. The Church has been extremely consistent on that whole "original sin, man is fallen" thing, and, honestly, if you take any period of human history and look closely at what's going on, you do tend to find a lot of nasty brutishness making life short. Meanwhile, various philosophies have come and gone, promising to reform us, make us all good and moral, end all the wars, etc. etc. And that doesn't seem to be working out so well.