Hmm, I would put it more as a lack of naive optimism about the future and a much harder world to live in than the one that was promised.
I was reading a biography of Ben Franklin & in early America people were having 8 kids, 10 kids, even 20 kids. That's part of how colonies were able to defeat the British, huge numbers.
Kids weren't considered a burden because they weren't, they were useful to the household. Modern culture treats kids as a nuisance that must be kept entertained and in their own world. Parents, children & grandparents are all in their own atomized universes.
I don't know about 'devaluing of human life and achievement' as much as life feeling shallow & kind of pointless for many people and being able to share a rich culture, community, values & inspiration for the future with one's kids is... well not something most people feel IMO (obviously I don't know how people feel but that's my impression).
Of course devaluing human life is fun & popular, the Bill Burr clip does a lot of that, but humans lowering self-esteem is not without cause. It's impossible to look @ the hubris of people from say the 1950's and not shake one's head. Watching Burr or George Carlin muse about how stupid the masses are isn't wrong, I would try to be an optimist and say tho that things are set up for people to be dumb/self-absorbed/ill-informed & that it doesn't have to be that way (but that corporations have us set up to be distracted & not particular capable of revolutionary changes), even this forum & my post at present could be said to be an example of that, I'd probably be better off trying to organize something in my physical community than opine flaccidly about global affairs but that would be difficult and I'd have to rally others who would be as tempted as me by their own distractions).
Absolutely, right now 'climate change' is thrown around without the layman (including me) really understanding it very well. Granted it's hard to put hard numbers on something that's in process but I think a more nuanced understanding of what it is, what we can & cannot do about it would help.
Altho I think the main problem is people don't trust government to actually do things about it. And why should they? People been giving lip service to solving environmental problems for half a century with minimal progress (a few electric cars, LED bulbs, not enough).
The depressing reality of modern society has already incentivizing people not to breed, that's what the thread is about. AFAIK the only country that has incentivized the opposite was China and that was some time ago.
The end of the century is a long way off & our global ecosystem is already pretty well f-ed (whether it can be 'fixed' is still unknown). 12 billion people dealing with converging global catastrophes is more complicated than 8 billion dealing with them.
Which political movement?
I notice the reverse of what you say, people who are pro-morebabies tend to be mostly be afraid of white extinction and similar nonsense. People who worry about overpopulation are environmentalist types who see the world as a whole ecosystem rather than being patriotic.
If you search 'Depopulation agenda' it's all right-wingnut fearmongering.
That's not really anything to do w sustainability just xenophobia.
But it's not surprising people are getting more nationalistic. Even people who ostensibly deny climate change probably in the back of their minds know they're wrong & it, along with geopolitical instability is gonna make migration orders of magnitude worse than it is today.
No easy answers.