I used to wonder that too, from reading about pyschopathy/sociopathy, and then later, Asperger’s syndrome. Then I got to know someone with AS, and they are worlds apart.
From what I gather, pyschopaths/sociopaths do not think anything is wrong with them, or the way they relate to other people. Other people exist merely to be taken advantage of. I get the sense from Gus Gusterson (and my stepson, who has Asperger’s) that they come to understand they do not connect with people in the the usual ways, and try to look for ways to overcome this. For example, from what I’ve read (most specifically, an excellent book called Without Conscience (subtitled) The Disturbing World of The Psychopaths Among Us. by Robert D. Hare, PhD) very few psycopaths/sociopaths ever seek out help from mental health professionals, as Gus did.
I also get the sense from Gus’s posts that he loves his wife as much as he is able to, just as I get the sense from my stepson that he loves me as much as he can. Is it the same depth of feeling I feel for him? Probably not, but everyone, not just people with development disorders, experiences love in different ways.