A sociopath has no ability to empathize and actually finds pleasure (sexual, or otherwise) from inflicting damage upon other living things, to include human beings.
How can a person feel nothing? There seems to be some explanation amongst the psychological/psychiatric communities that they are taught their behaviors. Some feel that they develop their inability to feel as a method of protection. Others feel that they are shells of human beings that are born without souls - I prefer the latter. Too much psychobabble can really get in the way of non-sociopaths attempt to understand. Whatever the reason/excuse might be, such behavior is intolerable, whether it comes from a spouse, sibling, parent, or child.