Since you raised concerns about the climate, I'm going to assume you agree with the concept that when people exploit the environment (e.g. nickel mines) it take

Since you raised concerns about the climate, I'm going to assume you agree with the concept that when people exploit the environment (e.g. nickel mines) it takes a long time for the environment to recover (thousands or millions of years). The environment is a resource for humanity since we need it to survive and it has a particular regeneration rate. Similarly, humans need the production of humanity to survive, let's call that the cultural resource. People who want to do activities and have adventures and travel to see things exploit this cultural resource to do so -- literally, in a second law of thermodynamics sense. Now, this cultural resource takes time to recover just like the climate, but unlike the climate the mechanism of regeneration is people. People create technologies, art, places, activities, adventures, medicine, and provide all sorts of goods and services. By doing so, they regenerate this shared cultural resource. Now, again, the population itself is a resource with a regeneration rate. However, people themselves exploit this resource primarily through their own birth and death, and themselves are the mechanism of regeneration through sexual reproduction. I assume that none of this is a surprise to you, but only that you might not think of them in this way of being resources and having regeneration mechanisms. Consider then that if you don't want the environmental resource to be exhausted (vs unrestricted free market capitalism) and you don't want the human population resource to be exhausted (vs death cults) but you also want to allow the free exploitation of the cultural resource (vs totalitarianism or the historical results of communism), then you need the people that opt-out of the population regeneration mechanic -- having and raising children -- to disproportionally contribute the maintenance of this mechanic and be happy to do so. If enough folks opt-out (because reasons) and are unwilling to help families ("alone and my way"), then that is demonstrably parasitic and exactly equal to voting for the collapse of the population. So let's talk about a 99% rate of defection (opting out). If you begin with a stable population in generation 1 and want a stable population in generation 2, then this population is demanding that the 1% of the gen 1 population regenerate themselves to create gen 2. This is tantamount to reproductive slavery. It gets even worse if those defectors are also unwilling to disproportionally support the population raising children. It will be a literal hell for those people. They would form a underclass worse than in the Handmaid's Tale. Literally farmed. So, at a 99% defect rate, it is objectively true that defectors, individually and collectively, are parasites of the environment, the culture, and humanity. At a 5% defect rate, it's probably tolerable. At 20%, one out of five, it's probably already unsustainable. The bottom line is that we all need to share the burden of having and raising children.