Both types of colonies could (and should) be pursued, but for self-sustaining colonies, the isolation that spaces colonies provide is an actual advantage. There

Both types of colonies could (and should) be pursued, but for self-sustaining colonies, the isolation that spaces colonies provide is an actual advantage. There's no incentive for self-sustainability with ocean colonies, because they can easily obtain what they need from the surface. Space colonies have clear incentives, because help would always be 6-12 months away (for Mars colonies).