Realistically, who goes to the trouble and tremendous risk of plotting to murder someone unless there's lots of hatred or lots of potential gain involved? I've never in my life heard of everyday people going around murdering any random acquaintance they don't like very much. I mean, how many people do you know who've plotted to murder someone just because they don't like them?
Potentially those with psycopathic or sociopathic disorders?
And no, you wouldn't tend to hear about "everyday" people doing this, because by definition you cease to be "everyday" once you start doing this.
But there are examples of mass murderers who don't appear to gain anything from the deaths of their victims, there are examples of people historically who it was "unlucky" to get to know, because their friends tended to have nasty fatal accidents. In some cases of mass murderers it seems almost to be a case of "why not murder them if I can get away with it?", although there may be deeper, hidden reasons that never came out.
I *do* also know a few people who've claimed that "if they could get away with it" they'd have killed people in their past. Hopefully they're full of hot air, and overstating things.
On the other hand, I don't know if realism would increase player enjoyment in this case: yes, it would be more immersive and make the characters feel more real, but for me at least, the characters *not* feeling real has always been a big part of why it's fun: crazy stuff happens and I don't feel to bad about doing evil deeds to them - because they're clearly not real. That makes it funny instead of sociopathic. I don't know, maybe immersion is better, but I can also see why a lack of immersion is sometimes better, also.
Realistically we have killers who have killed people apparently because they thought they had to kill one person born under each star sign.
We have doctors and nurse who have killed generally healthy patients in a variety of fashions, including overdoses, adulterated medication, simple deliberate bad care, inappropriate medication, or poisoning.
We have people who've kidnapped and murdered casual acquaintances and one-night sexual partners.
There are cases of people disappearing on highly travelled road systems and being found dead (or never being found again) with no sign of who disposed of them.
There are people who kill each other over losing a competition at their social clubs, or because of small continuous annoyances, or even "because he looked at me funny".
At the moment we have people on social media calling for certain people to be killed *purely* because they're in the same job as some other people who did bad things, and which has escalated in at least one case to attacks on their home, where their uninvolved family were living.
There are people who will threaten to kill you for being the wrong race, religion, or for hanging around with the wrong people. Or simply wearing the wrong colours and symbols in the wrong part of town - I once got threatened because I was wearing the wrong colour (plain, simple, off the shelf) bandana near a friend's house, to keep my hair out of my face (and more importantly the chain) whilst I repaired my push bike.
This last paragraph isn't so much "plotting" to kill people, but it is relevant in as much as you don't have to have *actually* done much to end up on someone's "I'm going to kill you if I can get away with it" list.
