You don't. People should have more kids, period. What people don't get about the declining birthrate is that it leads to a graying of areas and a huge economic malaise as the elderly consume more and produce much less in terms of resources. This is part of the reason places like Japan or Italy are struggling so hard...they don't have enough native workers to support their aging population.

The demographic death spiral can be real. And if anything, there will be worse environmental impact simply because you have to use more invasive means to support an aging population. More factory farms since there are fewer, older workers, more resource intensive automation and robotics to take over things people did.

Religion is not to blame, for most include proper environmental stewardship. Unfortunately that theme is being ignored in the developed world. How about simply making the argument that it is morally wrong to destroy God's creation?

Develop methods for turning people into atheists.

Consumerism, may be?

Edit: not to turn them into atheists, but to reduce birth rate.

You cant. Its game theory- those religions preach only what people want to here. And they want to here, that one of there descendants make it- so if everybody puts more tickets into the lottery, one has to gear the gambling up to have the same chances.

Also to thwart any racists- no, this is not limited to poor country's or certain skin colors. Once the economy drops below a certain threshold, everyone goes full survival zombie with the Loop-Deformation. Proof: The Nazis turned europe into a white version of africa during WW2.

The Nazis had their economy ticking over in a very productive fashion, certainly better than before their rise. A successful economy doesn't make people behave well, although it certainly makes it easier to. What do you mean by 'a white version of Africa'? There aren't many parallels I can draw.

Emergence of warlords/partisan leaders (Yes, for freedom, liberty, king & country, fascism - im sure, in somalia and afghanistan they have great causes too )

Soldiers of the leash. War feeding the war. Refugees pouring back and forth.

Source is mostly anecdata:

My late grandfather was a Nazi truck-driver in France, Italy, eastern Europe (Hungary, Greece) and the stories he and his war companions told - are really very similar to those you get to hear from African refugees. My grandfather and his officer made a nice little extra by smuggling people and got sentenced into a "Straf-battalion" for taking advantage of the general lawlessness of the situation.

I know, i know- the popular Nazi image in TV presents a wicked law & order extremist, but where the war went - it really was quite different. There was a mixture of total lawlessness (as in "We dont care/expend resources on subhumans") and extreme military overreactions.

And before you claim that was just fascism at work, as if politics where just a program loaded into humans, no,the unraveling usually set on before the occupation got started.

In a ironic way, the Nazis and their homecoming war proofed that all humanity, disregarding of race, pushed beyond a certain breaking point - is equally wretched and desperate.

A zombie like animal, forgetting about tomorrow, trying to see the end of today at all costs. Not a beautiful sight, but one that offers a lot to understand and learn.

The good news is, once the stress is reduced - and the war has not gone on to long, preventing the education of the next generation- there is a way to recover.

The Nazi economy was ticking over through the means of confiscating wealth from people, and later on, through just straight-up murdering them from it. It wasn't 'very productive', it was short-term gains with no long-term sustainability.

Compare the economy they had in the mid or early war to that in the early thirties or late twenties. Germany was in chaos. The output of their economy was still increasing throughout the allied bombing campaign. Duplication was removed, competition reduced, production lines simplified and available models decreased. Vulnerabilities were addressed and production went up, fast. And yes, by every measure I can think of it wasn't sustainable, but it produced a lot in a short time with extremely difficult conditions.

Again- similar "economys" have been seen in war torn areas of the planet.

I don't think the religions preach what people want to hear. They built procreation into their belief system to make sure they will have bigger and bigger adherents. It works and many of those religions are much larger today than others without procreation preaching.

Religions allow you to force a rule-set on your neighbors and limit your descendants behavior, long after they reached adolescence. I would guess for a middle-aged person, in constant silent fear of loosing it all with one mighty divorce - or drug accident of son/daughter - this sounds attractive.