A conversation with a reader begins thusly: "Does sociopathic behavior in an individual come from intense feelings of rejection from childhood? Could the lack of feelings or attachments to anything or anyone be a defense mechanism? And if they truly cannot feel love in the true sense of the word, why do they seek and pursue relationships?" My response:
Sociopaths feel love, just differently. I guess it would be like asking, why would blind people ever watch TV? But they do, they enjoy it for different reasons than you might, and sociopaths too find something worthwhile in love and relationships, not surprisingly. I would actually be more surprised to learn that there was any person who was completely uninterested in having some sort of a meaningful relationship. (Except maybe schizoids.)
With regard to your other question, I think most people now believe that there is a genetic connection to sociopathy, but that gene can either be turned on or not by environmental factors, e.g., as a defense mechanism, just like you say.