The established facts first, because the ethics only become interesting once the difficulty is honest.
ATMOSPHERE
About one per cent of Earth’s surface pressure, predominantly carbon dioxide. Unbreathable, and too thin to shield or to hold warmth.
RADIATION
No global magnetic field. Surface exposure to cosmic and solar radiation is hazardous over long durations; shielding means living under regolith or rock.
TEMPERATURE & SOIL
Averages far below freezing. The regolith contains perchlorates, toxic to humans and hostile to most crops without extensive processing.