Diversity of life it can support, shrinking, Earth not healthy, backfire? Just how exactly? I can’t see it and don’t understand what you are saying, besides that it is very alarmist and it seems on first view quite unrealistically so.

The Earth’s fragility and human capacity to damage it is
highly overrated in these times to put it lightly.
Highly overrated on what grounds? I’m perfectly willing to accept that climate change is part of a natural cycle occurring over millions of years, but that does nothing to diminish the fact that humans, in catering for our own needs and desires, have generally ignored the scale of damage we have been inflicting on other life forms, and have been all too willing to trust technology to ‘fix’ these problems for future generations of humans. The number of wilderness areas around the globe have drastically decreased during human history. Why? Because humans have cleared vast tracts of forest not only for living space, but for growing crops and raising livestock.
All very well, you might say. Why not do these things because we can? Well, why not indeed? Extinction of species, pollution of the natural environment and the atmosphere, depletion of soil nutrients, massive waste of materials… Of course, this is all fine and dandy if you think humans are the
only species with a right to inhabit the planet, but that would be kind of hard to support. Now that there are nearly 7 billion of us, how do you propose that the Earth go on supporting such numbers, especially given the likelihood that those numbers will continue to increase? Sure, the world’s population at present might fit into Texas, but as an argument against the problem of overpopulation, this one falls in a hole since it fails to take into account the area of arable land and the quantities of potable water required to meet such a population’s most basic needs.
Regardless of how you look at it, and whether you think I’m being alarmist or not, the facts of the matter all lead to the conclusion that we can’t continue to take advantage of the Earth as we have been doing, if we hope to preserve our species. Ignorance is not bliss - it’s just ignorance. Even small steps in the right direction, like installing greywater plumbing systems, growing one’s own vegetables, planting trees, choosing organic and free-range produce, recycling as much as possible, finding natural alternatives to harsh, synthetic substances - all of these things contribute to a more balanced, more humane coexistence for humans and the rest of the world.
There will, alas, always be people who think we should be able to take indefinitely from the Earth’s stock of resources, but hopefully they will ultimately be balanced by a sensible majority who have a care for the future as well as the present. You might notice that I am not advocating the destruction of the human race. We are living animals too, and moreover, we are animals with the capacity to minimise and sometimes even reverse the harm we cause to our surroundings. What’s needed is balance - we can’t just keep taking without giving back.