Yep, you can tell people all you want that humans need to get their acts together, but does it help any? Maybe there is another way.
I agree with what you are saying, that it is deeper than economics and a lot of the solution is ethics, but I phrase it differently. More importantly, I add one factor that might solve the problem. Like you, I despair when I explain the problem. It is listened to and understood, but no one can do anything. But there may be another critical factor, cheap and easy as would be required to change the story to one far more positive.
I'm a biologist, so let me tell you what you wrote but in my terms. I'll add two words to it that a biologist would and that is the only place I see hope. Like you, I saw this decades ago, have published one book on it (3 actually) and am working on the follow up.
My project is to describe how humans can adapt genetically and strategically for long term survival and development in the new ecology we have been developing to replace the hunter gatherer ecology we left for the farms and cities of civilization.
Ecology is a fantastic tool for organization and analysis of the problem, especially as the basic problem is adapting to changes in our ecology. Notice also that the difference between what you said and my mission statement is that I include genetics. I seem to have a knack for genetics and that's important here. What are you, I and so many others doing? We are wishing humanity would grow up some, maybe take their future in their own hands. I see one possible way it could happen and it's cheap, easy and aligns with instincts.
I'll describe this a bit backwards. My first book was "Genetics For A New Human Ecology". I'll mention it below. The second book, "Strategy For A New Human Ecology" is what I am working on now. I was looking at the current topic of population decline as I thought it would fit perfectly into what I work on. It raises the question of why to even have families. We only have so much instinct to have families, but we have great instinct to have sex, which naturally leads to families, except now with birth control. So I wanted to figure out what could release the "family instincts" that we see towards the end of many people's reproductive age. I concluded that a moral education, what you call ethics, would release those behaviors. Exploring a bit further into phislophy, I saw so many problems that society faces that could be solved or mitigated by teaching philosophy/ethics at a young age, as it used to be. (I'm currently working on what the curriculum could look like from grammar to high school. Don't mention philosophers or schools of thought, or the student will fall asleep as fast as when teaching American History.)
In philosophy, we have the information to solve the problem available. So how to convince them to use it? Well, like you, I never got any traction there, but I see a possibility... cheap and easy, as required. Also, the reason philosophy, the king of knowledge is no longer taught as anything but an archaic curiosity from history is that it has been completely crowded out by STEM. It was something of a casualty of the war between science and religion, but that is another story.
Anyway, the solution... may come from genetics. My book "Genetics For A New Human Ecology" is all about the danger from that we have removed Natural Selection, calling it human progress. That will lead to a unmaintainable genetic load of broken genes, particularly because of de novo mutations that occur every generation, that the parents didn't have. It's part of many problems like the 15% infertility rate, increased cancer rate, etc. Most chronic diseases are genetic based. Normally the broken genes would be removed, especially by disease, but not now. The technology exists and is being used in its infancy to replace natural selection with pre-implantation artificial selection. It is moral because it leads to healthy children and families, is not just for elites and it is necessary to human survival. Now the point of this is not about improving human genetics. It's about replacing the natural selection we have removed with medicine, but it will allow selection for "good" genes. Parents could choose to have their children inherit the best genes of both parents, somehting nature simply cannot do. Everyone could have health, beauty and brains. People wonder if their descendants will have the cognitive gifts to compete in the future. With artificial selection, they could accumulate "good" genes. It wouldn't be hard for it to lead to the minimum IQ being what we would call 100 today.
Now that's all well and good and may prevent a genetic disaster and may help us adapt to the new human ecology, but how does that help humanity grow up any? Why would that make them interested in the ethical strategies we have from history? Because when women are thinking about families, they take an unusual forward view. The instinct is there. Men too to some extent. If you warn them about the genetic disaster and they are seeing all these genetic problems and they are told that for no effort and a low price, their children could have just peachy genes, they would jump at it... Again, because the instincts are there to drive it, both reproductive and for status. If they got used to taking their genetic destiny in hand, they might then also think about taking their strategic destiny in hand as well.
That's my story and I'm not only sticking to it, I'm also writing it out in detail. The Genetics book is more up to date, but it you want to see an older vid on YouTube, look at: https://www.youtube.com/watch?v=wjVieFKevMk
I do believe humanity has everything needed to have a bright future.