Many social changes that have happened were basically unthinkable in the 1950's, the words literally did not exist to describe them.
The author disagreed with that, saying that predicting future technological changes is not really important. What is important is predicting the social effects of those changes. That's what a good science fiction writer should be figuring out.
They gave an example that went something like this. Imagine someone writing a science fiction story in say 1890 (although I suppose it might not have been called science fiction yet) set 100 years in the future in the United States.
Predicting that people in 1990 would have horseless carriages instead of horses, and they would be widespread enough for nearly everyone to have one is interesting, but according to author not really insightful.
The useful and insightful prediction would be for the writer to figure out, say, what affect that mobility would have on teen dating. In 1890, most of a teen's social life would involve other teens who lived within easy walking distance plus maybe some farther away that they met at school and either only socialize at school or at activities that are close enough to be in reasonably walking distance for both.
But in the future, when families have more than one horseless carriage and that teen has easy access to one, their social life can involve anyone in town, or in neighboring towns.
Also that 1890 teen that has to walk everywhere might have limited opportunity to get of parental supervision long enough to be alone with their boy/girlfriend. 1990 teens with their much greater mobility can much more easily get away from prying parental eyes and get up to things that would be scandalous in 1890.
And in the end, it didn't really matter that much, since most teens only dated people in the same school, church or other social institutions they attended anyway.
'Ethnic group' is the primary criterion. That would correlate race, religion, language, culture all into one.
We think we are now 'very moral' but I'm doubtful of that. If you want to play the devil's advocate it's not hard to point out obvious hypocrisies in much of our current social line of thinking. During any era of 'change in one direction' all arguments in the opposite direction or all arguments that have nuance and don't 100% back the current populist trend are utterly oppressed as 'vile'.
Alcohol is an interesting one that goes through phases: prohibition was hand and hand with women's suffrage because 66% of men were wasted every day or every few days and either not coming home, or beating their wives. Without that social context, we look at alcohol differently.
So there's comment here about 'how technology changes people' which is exactly right.
The big one is not how 'horse and buggy' affects dating, it's how contraception has affected us.
50 years ago - sex almost instantly led to children - period - no debate. If your daughter was sexually active, she would be pregnant almost immediately. Your son would technically be a father. This has vast, vast social consequences that affect every part of life. We now have a lot of 'sex positive' people who're ideology wouldn't really even be fathomable just a generation ago, let alone popular. Contraception is as big as the combustion engine.
This article has a lot of interesting detail, going back to antiquity. It really started to pick up steam in the mid 19th century.
https://en.m.wikipedia.org/wiki/History_of_birth_control
One interesting detail is that the sudden drop in birth rates that happened around the introduction of the pill also happened in countries where that never became a very popular method of contraception, Japan being an example.
Around this time, due to commonly available forms of contraception: the nature of sex changed, family roles changed, the workplace changed, gender roles changed, birth rates plummeted, demographics changed fundamentally, family structures changed fundamentally.
Aside from real-estate - a family could live on one income if they wanted to give up all of those things.
I'm not entirely disparaging your point, other than to say the entire system has changed, it's not like 1950's standards now cost 2x.
But yes, surely it's a weird artifact of classical liberalism that 'freedom' is somehow implied to be 'now you have to work for money or starve'.
Edit: I should add, that by any economic definition, if during one era only 'one parent' is working, and during a different era 'both parents' tend to be working, it's just a mathematical reality that those with only 'one parent working' will move down the economic ladder relative to others. This would be true before a single sociological artefact contextualised the fact.