At cafeterias when I was a lad, bowls and plates were stacked into tubes with a spring-loaded platform at the bottom. As you took your plate off the top, the stack would rise accordingly. In the short run, it seemed a sort of magic to a boy: there was always a full stack of plates, no matter how many you took.
Something similar happens in improving the justice of American society. We take off a plate and there are handshakes all around. A poor man can prevail in court if he is right. Hey, people can keep their property even if they are Quakers. The woman of the house has authority over the farm when her husband dies, even if her sons object. A free black man can vote. A woman can become a doctor.
On and on goes the list of increasing justice. Plates keep coming off the top. Yet to each generation, the stack looks the same. How could you? This injustice has been going on for centuries and America did nothing. Only in our new moral age, which began last Tuesday, have there been people who really understand justice.
We quickly take standard-of-living improvements for granted. We forget how poor even Americans were in living memory. An easy-to-remember set of numbers: In 1949, 41% of Americans lived below what we later defined as the poverty line. In 1941, 49% of Americans were below the poverty line. And that was after the Great Depression was over. Death in epidemics remained high. Medical care was mostly useless.
The politics of outrage knows no history. So you had starving children, and relatives dying in pain? What of it? You came to America because no one would kill you for being Jewish, or Laotian here? Too bad. Get with the program because people are really suffering today, having to pay for their own birth control and being spoken of disapprovingly for their sexual behavior. It just proves that America is racist because we can still find some racist people.
CS Lewis mentions it in Screwtape, that what a human being comes to expect he rapidly convinces himself he deserves, and is put out of sorts when he doesn't get it, however little he has done to earn it.
It might be argued with a bit of fairness "Well, fine then. You did those wonderful things and now we are down to the last few things that need to be made fair. What's stopping you now?" I have seen a few answers, but here is mine: we are down to ambiguous cases. There are competing values, not merely interests and traditions. It's tradeoffs from here on in. If you can't see that government paying for abortions; or affirmative action; or women in combat; or a dozen other things we argue about are ambiguous, then I must conclude you are not a deep thinker.
I long ago said that in much of depression, people are first depressed, and then attach it to life circumstances. The paranoid style comes first, then goes looking for conspiracies. I think social justice outrage comes first, then goes looking for causes. That's not necessarily all bad. A subset of the tribe that is hyperalert to underdog-rooting probably improves the general lot. But it's a good thing only insofar as it counterbalances societal inertia. It's not a stand-alone virtue.