I was thinking about a special module that gives you 500 passive defense as long as you haven't performed any offensive actions in the past 24 hours.

Another idea:
Hospital: (Planetary Building)
Size: 2
Population: +50, & +10%

these are good idea's, but i got 1 question, how would these be obtained? GL points? certain mission, NPC, etc (rare, extremely rare? etc)

No offensive actions within the last 24 hours means you are able to use Halcyon Traps and Calming Amplifiers. That is essentially 6 hours of INFINITE defense. Throw in Trinity Drives, Gemini Cannons and Xecti race bonus and we have more than enough "pansy defense."

Astrobiology Ward: Size 1, Population +500, Population Bonus +50% You would need either 8 stacked Hospitals (16 spaces) or 1 Hospital and 1 Trans-Hub Habitat (8 spaces) to have a comparable population to just only ABW by itself.

Total score: -2

Touche Darth Flagitious, now that u mention it, this is a bad idea