No, that's a quite recent development too. Not too long ago it was normal for each household to have one earner. Now, thanks to women joining the workforce, we all work more for the same thing.
No, we work more for more things. If you were to live according to the living standards of the times we associate with stereotypical one income households, say 40 years ago, your house would be 1000 sq feet smaller, your electricity consumption would be much lower because you would have no smartphone, a small TV, your car would not have the features it has today, you would likely have no college education, and your healthcare expenditure would be lower because you would receive significantly less care. You also would sweat a lot in the summer, because back then air conditioning was a luxury rather than the rule.
You would also eat significantly less meat, and you would be much less likely to go on holidays, travel abroad, or eat fresh fruit from the other end of the world at all times during the year.
A big part of why we have more is social & technical progress. We get more for our money.
I do think your parent's question is an interesting one- thorny, but it's not ridiculous to wonder if doubling the work force eventually gnaws away at compensation for the same work. (The natural next question is, well did the demand for labor grow to match, stay constant, or somewhere in between? Did the pie grow and we're all wealthier for it, or are twice as many people now fighting over the same pie?)
A larger labour force means more competition in wages, but it also increases supply so this shouldn't have any effect. If this wasn't true, then you could reduce inequality simply by artificially restricting the supply of labour, which I don't think has ever occurred.
You've got to be joking. My grandparents lived in much bigger houses with much more land than I could ever afford despite the fact that they were single earner manual labourers and I'm a highly qualified person with in STEM.
In any case, they were at least as happy with their cars then as we are now, and they didn't want smartphones.
http://www.aei.org/publication/new-us-homes-today-are-1000-s...
You happen to be an outlier if you're living in a smaller house than your grandparents. Given that you're saying you're a STEM worker and that your grandparents were manual labourers, my guess is that they owned cheaper property and you live in a very urban area. Which has very different perks.
Smartphones use a ridiculously small amount of power compared to many of the appliances people had in those days. Modern TVs also use less power than old ones.
No, electricity consumption would be lower because you wouldn't have air conditioning. That's the big power user in most peoples' homes.
The only people to whom a single-earner household outside the upper and upper middle classes was ever considered a default were the inhabitants of certain developed countries for a few decades in the middle of the 20th century; and even then it was more of a norm than a universal fact.
The only things that changed recently are a) women now can also have "careers" and prestigious occupations instead of just jobs; and b) working outside the home has become normal for upper middle class women as well as working class women (and for some even a status symbol rather than a symbol of poverty).
Edit: Just as soon as I post about not seeing the connection, I find the bit they were referencing:
"6. The Two-Income Trap, as recently discussed on this blog. It theorized that sufficiently intense competition for suburban houses in good school districts meant that people had to throw away lots of other values – time at home with their children, financial security – to optimize for house-buying-ability or else be consigned to the ghetto.
From a god’s-eye-view, if everyone agrees not to take on a second job to help win their competition for nice houses, then everyone will get exactly as nice a house as they did before, but only have to work one job. From within the system, absent a government literally willing to ban second jobs, everyone who doesn’t get one will be left behind."
CAGR from 1971 to 2018 - 5.5%