Could Life Exist Under Very Different Conditions?
All known life exists on Earth. Our understanding of habitability is therefore based upon a single example.
Life elsewhere might tolerate environments very different from those found on Earth. It might use different ecological strategies, inhabit subsurface oceans, survive beneath ice, or occupy environments that would be hostile to familiar surface life.
If life can exist under a much broader range of conditions than we presently recognize, Earth-like conditions may not be as unusual or as necessary as they first appear.
Why This Matters
If radically different forms of life are possible, calculations based only upon terrestrial organisms could underestimate the range of habitable environments.
This is especially important when moving from the modest statement that Earth is suitable for known life to the much broader statement that certain conditions are necessary for any life.
Our evidence is strongest when we clearly distinguish those two claims.
Response
This possibility should remain open. Astrobiology itself attempts to distinguish the requirements of terrestrial life from broader conditions that might support life elsewhere.
At the same time, speculation about unknown forms of life cannot establish that virtually any environment is habitable. Every known example of life depends upon complex chemistry, usable energy, suitable materials, and an environment in which organized biological systems can persist.
The responsible approach is therefore to begin with what is known from Earth while recognizing that future discoveries may broaden our understanding of habitability.
An Intelligent Design argument should not require extraterrestrial life to be identical to terrestrial life.
Question That Remains
How different could life be from terrestrial life while still satisfying the physical and chemical requirements of a complex, organized, reproducing system?