Also bluntly: how would we do that ethically without severely restricting reproductive rights or "cleansing" populations?

Because I don't know what the solution is but I do know that the alternative is going to be no fun at all. One possibility is that we all end up agreeing that we should at least try to reduce our numbers. My parents brought me up with 'replacement' numbers so that we'd end up with a steady population. I'm not so sure if that was wise. And I'm aware that there are many predictions out there that our numbers will eventually top out (they will, either because we do it ourselves, voluntarily or because our resources will run out, an exponentially expanding population in a fixed environment always ends in collapse).

But unless we manage to reduce our impact on the environment in very drastic measures I don't see a way for the increased consumption and eventual survival of our societies as we know them today. In another comment someone offhandedly asked whether we should all want leisure yachts or not. The obvious answer to that is 'no'. But we probably also shouldn't all want vehicles and the ability to transport ourselves to the end of the world on a whim. Hard choices are ahead of us, the time for easy answers is long behind us.

Nature will be wanton, cruel, perhaps overshoot. It will be ugly and horrific. We will not be left in great shape. The only fairness it will possess is unpredictable randomness.

Or, we can do it. Harsh. Belt-tightening. Unpleasant conversations. Lengthy debates about worth. Whole societies wanting their turn at the trough. Deprivation. Lifeboat politics. The Cold Equations in a hot, hot world.

Everybody who decides that what they need to do is kill extremely large numbers of other people can just off themselves instead.

And so the scavengers will feast and the plagues will bloom again. And because no-one will agree, we will have little local wars over resources. Maybe someone will grab a warhead or two. Technology still keeps happening, so expect at least one plague to be targeted. And some group will have a "if we can't have it, nobody can," so a self-irradiated country will get to keep a resource out of some other group's hands. You'll get real genocides, then.

Nobody wants to participate in the one way of getting their hands bloody, pretending that they won't get bloody later on, up to the elbows.

Uh, no. I'm watching this garbage truck smash into the wall, same as you. We're all in the same boat.

We could easily be in 'adapt or die' territory somewhere in the next century.

I hope it's clear from context that I wasn't directing anything at you; we're basically in complete agreement.

The majority of people around me would rather invest in holidays and luxury goods than sustainability and aim to increase their footprint rather than that they reduce it. I'm just as guilty because I too live in a wealthy country. And even though I bike when I can and have spent a small fortune on making this house less dependent on outside energy I make myself no illusions: I'm still a net negative on the environment, far in excess of any developing world denizen. All I have to do to have that reinforced is to look at our trash can, food bill and fuel bill for the times when we do drive. Each of those alone is probably well in excess of our 'proper' budget that would be sustainable.

And for the life of me without stopping all activity I have no idea how I can further reduce it, this is just the world I happen to live in. I guess I could not have had kids, I guess I could live in a tiny shack. But overall everybody in the developed world will increase the problem by virtue of being alive. That's not good news, but I don't have anything better.

Rich people consume orders of magnitude more resources than poor people so if anything it's unethical for rich people to have children.

Exactly. The dismantling of Roe v Wade in the US comes to mind as a form of severely restricting reproductive rights.