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Well an idea might be to give one more stat to colonists..empathy or alignment. For instant Bob could be mild mannered, and easily offended, where-as Matilda liked killing bugs as a child..
This could make the game(or your colonists) have some real issues getting along, enjoy the carnage...or go plant flowers in hope of peace. Banding with other like minded groups would come more naturally as well.
This could lead to new character traits as well, ie psychologist, criminal, devious, saint...ect.
New buildings/equipment/items

Yeah, I like the idea of giving them more stats and character traits, it seems like it would be the way to go about getting it done.
With that said it would make things more interesting if Jimmy and Carol were accepting of being cannibalistic and word of this would spread to other colonies which would with time attract colonist to your colony to join or anger a different colony. Maybe even change the way their fellow colonist think.

There needs to be some kind of diminishing fear and unhappiness. I'm tired of my 3 original colonist burying the 50th body and still getting smacked with full -happiness. What I think would be good is that as time goes on or for every body seen/buried that the will slowly get use to it. This would probably go for cannibalism/human rugs/blood/wounds/ect. If I want to choose to have a cannibalistic colony, they should learn to get over/accept it. We should not have to worry about losing our starting colonist several hours into a game due to things stacking up like -seen dead body -ate raw food -ugly environment.
Another thing there has to be is more things that give +happiness such as +doing burning passion +seen friendly face +well rested +successfully defended colony, the list of possibilities goes on and on. Feel free to add more ideas, -/+ fear would be good as well to see.