That's not defeating of aging until you found a way to prolong youth and not just the old age as this research seem to assume.
The article considers four separate cases: 1) negligible senescence, 2) slowed aging, 3) continuous rejuvenation, and 4) one-time rejuvenation.
It seems that at least 1 and 3 are what you want. Have I misunderstood your comment?
EDIT: thriftwy is correct, here. The authors leave the crucial detail of when, in their model, life extension begins, until deep in the article. It's around age 60, in their model. This is in no way what is conventionally meant by these terms as I have ever seen them used when reading about "negligible senescence," "anti-aging," "SENS," & etc.
EDIT: Ah. They explain that later in the article. That's an unfortunate use of the term, given its history of use in the field.
(as long as we're just making up future scientific advances)
In 60-s, people imagined how population would line up for space colonies to build a farm there. And a big house.
Now, people want not just live on Earth. They would prefer to live in, let's say, the EU. And not even all of the EU; how about a Paris arrondisement? That's the place we find desirable.
A few people would like to be the first to space colonies. I fail to see how a few billion people would like to move there, to become some sort of worker drones. Plus, this tend to not end well. Compare how well do people in Spain live, and compare it to how people who went abroad to South America live.
The fate of South America is not due to the failures of the local population... more "thanks" to decades of racist and/or anti-"communist" US foreign policy.
Admittedly, I did not fully understand the point the GP was trying to make with the Spain comparison.
This will be the case with space colonies too, I'm afraid. While it will be debatable why colonies perform worse than Earth, it will be apparent that the best course was to stay.
I don't know many fellow Americans that are of Norwegian descent but the US fairs better than the UK on lists of human development, happiness, and productivity. That has to mean something.
Current examples are the rapid growth of Orthodox Jews as a percentage of Israel’s population, and evangelical birth rates in the US.
My bet is that given technology to allow massive extension of fertility into older age, the fertility differences between religious groups that believe in a religious duty to procreate, and everyone else, will increase even more.
I like to joke that the Amish are obviously the one true religion because eventually they'll cover the earth: They live long and peaceful lives, have scores of children, and are among the best farmers on Earth.
As long as the rest of us don't do something horrible the end state is inevitable.