The point is not that this world is too sad to love or too glad not to love; the point is that when you do love a thing, its gladness is a reason for loving it, and its sadness a reason for loving it more.
And (!)
All optimistic thoughts about England and all pessimistic thoughts about her are alike reasons for the English patriot. Similarly, optimism and pessimism are alike arguments for the cosmic patriot.
Would be nice to live in a place where people were like that, rather than the world of infinite groundlessness and choices, where we are everywhere and nowhere at once. But that's the rub to Chesterton. First sacredness, then civic possessiveness, then invest in community:
If men loved Pimlico as mothers love children, arbitrarily, because it is THEIRS, Pimlico in a year or two might be fairer than Florence. Some readers will say that this is a mere fantasy. I answer that this is the actual history of mankind. This, as a fact, is how cities did grow great. . . Men did not love Rome because she was great. She was great because they had loved her.