If we invert the current infrastructure-first and survival-hedge framings and instead treat a strict ban on creating new, hard-to-exit political communities as the baseline (on Earth and off), what follows for space colonization policy: under what empirically testable conditions, if any, should we make narrow exceptions for large orbital, lunar, or Martian settlements, and does this prohibitionist lens imply that many proposed Earth megaprojects (e.g., charter cities, floating habitats) are ethically on a par with or worse than Martian city plans?

Answer

Treating a ban on new hard‑to‑exit polities as baseline yields:

1. Default policy

• No new large, permanent, self-governing communities that people cannot cheaply leave, on Earth or off.
• Space projects: small, rotating outposts and infrastructure nodes only, under strong external law.

2. Conditions for narrow exceptions (all must be empirically supported)

Cross-cutting (Earth and off-world)

• E1. Exit cost bound: verified practical ability for most residents to leave within a fixed time and cost band comparable to major international migration.
• E2. Health floor: evidence that long-term residence is not substantially worse than harsh but acceptable Earth environments.
• E3. Governance test: audited non-domination safeguards; no single actor can use life-support, housing, or borders as coercive levers.
• E4. Benefit over alternatives: independent analysis shows the project does more for survival/justice than best available non–polity-building alternatives.

Location-specific thresholds

Orbital settlements

• O1. Artificial gravity available to all; radiation within agreed safe bands.
• O2. Frequent, affordable transport; real return/rotation rights.
• O3. Governance integrated with Earth law; high reversibility (stations can be de-populated or repurposed). => Conditional permission for large habitats mainly as infrastructure with strong rotation norms; fully closed, permanent orbital city-states are disfavored.

Lunar settlements

• L1. Verified health data for low gravity; robust shielding.
• L2. Regular, not-exorbitant launch capacity; practical mass return.
• L3. Strong external leverage and multilateral licensing; scale caps tied to exit and oversight capacity. => At most, medium-scale towns with easy rotation and exit; bans on fully autonomous, hard-to-exit lunar polities.

Martian settlements

• M1. Much stricter health evidence (partial-g, radiation, reproduction) before allowing multi-generation residence.
• M2. Very high self-sustainment before large populations, but combined with guaranteed Earth leverage that cannot be used to threaten basic survival.
• M3. Quantified survival advantage: models show large Martian settlement materially reduces existential risk more than Earth alternatives. => Under a prohibitionist lens, large Martian cities are allowed only if (a) survival benefit is clearly demonstrated, and (b) domination and exit harms are empirically kept below strict bounds. This is a very high bar and likely not met for a long time.

3. Implications for Earth megaprojects

• Many charter cities, seasteads, or floating habitats would also be banned by default: they create new, semi-sovereign, exit-costly polities.
• Where exit is cheap and rights are strongly protected (e.g., experimental charter districts with guaranteed national/EU-style protections and funded exit), narrow exceptions may be possible.
• Projects that deliberately raise exit costs (isolation, employer-tied visas, company housing monopoly, transport control) look ethically worse than tightly controlled Martian or lunar outposts, because their harms are immediate and large-scale while survival gains are minimal.

4. Are Earth megaprojects ethically on a par with Martian city plans?

• Under this lens, large Martian cities and serious Earth charter-city/floating-city schemes are in the same risk family: hard-to-exit experiments in new political orders.
• In practice, many Earth megaprojects are closer to being ethically unacceptable now, because: • They are easier to build soon. • They can entrench domination over large vulnerable populations quickly. • They lack significant survival or global public-good upside.
• A distant, speculative Martian city with strict global vetoes may be less urgent but still presumptively disallowed until the stringent survival and governance tests are met.

5. Policy summary

• Strong presumption: no new hard-to-exit polities, on Earth or off.
• Space: small, supervised nodes; narrow, tightly conditioned exceptions for larger orbital/lunar communities; very restrictive stance on Martian cities.
• Earth: major charter/floating-city schemes treated as ethically comparable to or worse than Martian city plans unless they prove low exit costs, strong external rights protections, and clear benefits over non-polity alternatives.