Honestly, I don't know how doomerism has survived the long arc of history. We used to grovel under kings. Slavery was the law of the land. Fascist authoritarians conquered a democracy and declared war on a continent and a people.
And, all of that was overcome. It ceased. History didn't end.
It's not even a myth! It was a rhetorical statement!
MLK didn't actually believe that the world would get better (well maybe he did), the line was to shame people into joining the cause!