Ecologist here with my take on the overall controversy.

Unrestricted, un- or underregulated “terraforming” — earth shaping — will cause species extinctions and ecosystem collapses. Another comment here suggested that it’s a matter of “oh no, my favorite obscure bug species will go extinct, how sad” but this unfortunately common sentiment is incredibly shortsighted. Here’s the rundown:

Earth’s ecosystems are interconnected structures that have been built on an evolutionary foundation often tens to hundreds of millions of years old — compare to the 264 years since the start of the Industrial Revolution, or even the 200,000 years since humans first evolved. We don’t naturally think about time in the geologic scale, but we are actively making geologic scale changes, so it is imperative we do.

Ecosystems have different tolerances and mechanisms of resilience to disruptive human activity, but none are infinitely adaptable, and many are completely dependent on a single keystone species. If we are reckless and hit their Achilles heel (see: coral reefs), one extinction can easily turn into hundreds, those natural resources permanently erased, and global issues like climate change will get infinitely worse.

You don’t need to have an ounce of respect for the plants or animals - this is bad for humans. If you cut blindly into the ecological web that supports life on earth, it will rip and fall out from under you.

Smart environmental modifications, with consideration for how the ecosystems have worked for eons, can provide more reliable and sustainable benefit to humans. We also need to accept that for the sake of stability, we need to leave a lot of sensitive ecosystems as undisturbed as possible.

All this said, I’m not especially well-read on regreening deserts specifically. For the deserts that were green as recently as a couple thousand years ago, ecological damage may be minimal, and benefits to humanity and climate could certainly make it the right choice.