We need both emotion and logic for empathy We need to understand that our actions cause pain and pleasure to other people (and animals--but that's a different debate) by relating through our own emotions and nerve endings.
The intellect sorts out these sensory experiences and allows us to communicate with others about fair compromises and mutually agreeable exchanges, or to get a grip on our own emotions if they begin to confuse us.
Emotion is the basis of even the most superficial levels of courtesy and etiquette. Think for a minute on why it's rude to fart at the dinner table. Or why it's excessive to slap somebody who just farted before they got halfway out the kitchen. Neither act is physically damaging to anybody else. It's not so much about logic or physical pain, but to make up for the fact that over 85% of us emote in consistent ways. Codes of etiquette exist to prevent messy, distracting and time consuming emotional outbursts over trivial problems like bad smells and pushy behaviour.
Universal morality? Absolutely not. But reasonable codes of conduct that are agreed on by all parties in a given group, and reasonable attempts at following them are required for workable social dynamics.
Murder is wrong bc it pisses people off and provokes years, sometimes generations or centuries of retaliation and counter retaliation. The former Yugoslavia, Gaza, etc. etc.... History is full of proof as to why murder is wrong.
*Note: not all types of killing are considered to be murder. Again, this is a code of conduct that is agreed upon by a vast majority of individuals across different cultures. The rules do vary from culture to culture.
Blah. I don't feel like googling for specifics, so I'll give you the difference between sociopaths and psychopaths from memory. Excuse me if my storyteller's grasp isn't what a research psychologist's grasp would be (I came here to flesh out characters for my story/stories not to reinvent the pcl-r :P)
In a nutshell, psychopaths and sociopaths experience shallow emotions, but psychopaths tend more often to be prone to delusions. The case studies I've read suggest that psychopaths will sometimes kill bc of compulsions that I have yet to understand, or bc of deeply flawed beliefs about love. Sociopaths have a better grasp on measurable realities that can be verified by third party consensus. Sociopaths lie and manipulate and will sometimes kill, but there is more often a practical, territorial, or financially motivated goal behind their destructive acts.
The relationships between agreed upon realities vs. faulty perceptions vs. temporary lapses in observation vs. clever embellishment vs. destructive manipulation could go on for days...
So feel free to split hairs. I may have to come back to this in a few hours, tho. My time isn't really my own today.