Negative morality is gained by killing humanoids (kobolds, bandits, swamp orcs), killing animals (Boars, scavengers, cave crawlers, wild dogs, boglings), drinking alcohol, smoking, doing drugs, rejecting to help random event NPCs.
Again, this is because the system is, like most systems in the game, unfinished. To be evil, you pretty much have to avoid doing a lot of activities, because they raise your morality. Being good on the other hand is quite easy, since you get good points for pretty much anything and abominations are easy to grind.
All of this will change in future versions as there will be more ways to be good or evil. I will also add some kind of perks that affect your morality in some way.