Lifeless planets must be terraformed (if/when it will be considered feasible/necessary). Human needs are greatly overweight the "sacred" planetary chemistry and geology.
I'm an anthropocentrist, I'm all about human-need. My issue is that if terraforming even is within human interest, as it's also human-need to preserve the environment for research, and study but lets go deeper. I don't mind exploiting it for resources, and extracting ores and minerals, but covering half the planet in water barely seems like a reasonable reaction to creating a habitable place to live. I'm not speaking against colonization, I'm against terraforming for the sake of colonization. It feels like completely going overboard for the sake of a simple need-- habitation-- in sacrifice of a whole LOT of other human needs like research, stability, and efficiency of growth.
People seem to underestimate the level of scientific research and knowledge that can be gained from planets in other solar systems. It comes from the ignorance of biocentrism, and the idea that inanimate matter is not complex, and research of inanimate matter is not hugely beneficial towards humanity. May I list just a few of the scientific disciplines and sub disciplines that have to do with the study of inanimate matter, that would hugely benefit from trying to maintain a planetary environment that develops in unique conditions: Physics (Pretty much every discipline), Chemistry (Inorganic Chemistry, Environmental Chemistry, Astrochemistry), Oceanography (think about methane seas on titan, or ocean planets), Atmospheric Sciences (Metereology, Climatology, Atmospheric Chemistry, Atmospheric Physics), and so on and so on. I haven't even mentioned geology and the geosciences, things like Water science, minerology. And what would make the complexity of these disciplines diminish in the future? By the time we arrive to these planets, we'll have far more questions than answers that would last an indefinite amount of study.
Just look at the list of unsolved problems in geoscience to get an understanding: https://en.wikipedia...s_in_geoscience
The thing about changing the composition of a planet's entire atmosphere, as well as the geology (water alone would transform this), and the reaction between land and the new atmosphere, as well as from the actual process of terraforming (as that would require either a vast extraction of resources of the planet to develop an atmosphere or remove an atmosphere or the addition of resources from out of the planet to develop a new atmosphere) is that we don't know definitively what will happen. What if it causes a chain reaction that leads to disaster, what if it's accidentally toxic to the life there. No matter if these examples seem stupid (even though that's exactly what's happening right now with our own planetary exploitation), it's about the possibility of something going wrong-- something that could happen, even to our omnipresent descendants.This wouldn't lead just to an isolated issue, it would lead to a planet-wide issue that affects every person on the planet they're inhabiting and colonizing.
Just think about all the proposed methods of terraforming mars. Nuking the ice caps, or building a giant artificial magnetic field, or leading asteroids towards the planet, or literally mining the whole surface to release CO2. Does this sound entirely stable? In fact, this strain of arrogance towards an environment by supporters of terraforming is exactly what's causing our current environmental crisis.
And lastly, would it really even be wise to use so much resources towards terraforming, when our energy and resources could actually go towards resource extraction and the construction of isolated habitable environments. Terraforming a planet requires such a giant concentration of energy, resources, and power, towards something that doesn't benefit anything past providing a place to breath-- something that we can already do with isolated environments-- or exploring the environment-- which we can do with suits we can create and we can expect to create far better than now. What about creating an earth-like planet for research? We already have an earth-like planet for research where life developed for billions of years. Building another earth-like planet for research when its developed for a few centuries, hell even tens of thousands years is ignorant of how long it actually takes for life to develop and will do little in the way of profitable research that can't also be done in small isolated environments.
It's a waste of resources towards actual colonization and growth, things like asteroid mining, resource extraction from planets, construction of habitats to house humans in the present and not in the hundreds-of-years later.
Lastly, the gradient you provide is ignorant not just of the inorganic sciences, but organic ones on well, which adds another level of complexity, and my argument carries on from there as well.