>It's easier and much more efficient to get resources such as raw materials and metals from the ground. Being in the air without option of landing means you are completely dependent on import of raw materials to repair/expand your habitat. Very inefficient as well as not economical.
Assuming you overcome all the other difficulties and have a colony on Venus' skies, what prevents you from having ships that can go to the ground, get stuff, and come back?
Assuming you overcome all the other difficulties and have a colony on Venus' skies, what prevents you from having ships that can go to the ground, get stuff, and come back?