Are We Just Making a List of Earth's Features?
When we ask why Earth is habitable, there is a danger of simply making a list of characteristics Earth happens to possess and then treating each one as though it were necessary for life.
Earth has a large Moon, plate tectonics, a magnetic field, oceans, continents, a particular atmospheric composition, a particular rotation rate, and many other characteristics. But the fact that these features occur on an inhabited planet does not demonstrate that every one of them is required for an inhabited planet.
A different world might achieve long-term habitability through a different combination of conditions and processes.
Why This Matters
This objection goes directly to the method used in a habitability argument.
We must distinguish between a feature that contributes to Earth's present environment and a feature that is actually necessary for long-term habitability or complex life.
Without that distinction, an investigation can exaggerate the evidence by counting every familiar characteristic of Earth as an independent requirement.
Response
This objection is well taken. We should not assume that every characteristic of Earth is individually required for life.
That is why this investigation distinguishes established requirements from proposed advantages and uncertain claims. Liquid water is fundamental to all known terrestrial life. By contrast, the necessity of a large Moon, an Earth-like magnetic field, or Earth-style plate tectonics is considerably less certain.
The more important question is cumulative. What combinations of stellar, planetary, atmospheric, chemical, and geological conditions can produce and maintain environments suitable for complex life over long periods of time?
The case should rest upon what the evidence establishes, not upon turning Earth itself into an arbitrary checklist.
Question That Remains
Which characteristics of Earth are genuinely necessary for complex life, which merely improve habitability, and which are simply consequences of Earth's particular history?