Looking for advice on how to construct a science fiction scenario/story/campaign

Is your party playing "good guys" as per DnD allignements a necessity ? (like something you want to run or something they want to play). If not, Science fiction might be a good occasion to change that.

Having your players not be "good" doesn't mean they will be evil. It can just mean they are playing people with average morality, ranging from the random guy who is a bit opportunistic but not a ciminal, to the one who is a "space cop" but not a paladin, dying to go purge all evil.

This allow you to have antagonists be far more nuanced, which is in my opinion more interesting, and more fitting to what you seem to aim at (because as you said, replacing the demons with evil civilisation-eating aliens won't be a big change).

/r/rpg Thread