The design of space habitat modules critically emphasizes life support systems to sustain human life because these systems are essential for ensuring the survival and well-being of the crew. Life support systems encompass a variety of technologies and processes that provide necessary resources such as breathable air, potable water, temperature control, and waste management. Without effective life support systems, a space habitat cannot function for extended periods, especially in the harsh environment of space where resources are not readily available.
Focusing solely on aesthetic considerations or elements like propulsion systems does not address the immediate need for human survival in a space environment. While weight is certainly a factor in spacecraft design due to launch constraints, it is secondary to ensuring that the habitats can maintain a livable environment. Hence, life support systems represent the most vital aspect of designing space habitats, allowing missions to be conducted safely and effectively.