In point of difference to those pointy heads out there, who learned pseudo-science from TV shows like Criminal Minds, and or a video game character with a video game BA, Kelly Chambers. Jack shows no signs of being a sociopath, at least not in accordance to the clinical typology I once studied in psychology and sociology. Jack shows "some" signs of Anti-Social behavior, like those found in Episodic Dyscontrol Syndrome (EDS, which is usually attributed to a mixture of biological imbalances, and early childhood trauma etc). However, Jack, like say Tomas Harris' Hannibal Lector, does not fit the criteria of what a sociopath is in reality (think of Lector as the Hollywood version, that people for whatever odd reason get all hot and heavy for). I would argue that Jack fits the psychological fiction found in our culture, up to the point where the fiction is a misapprehension of science.
Psychopaths are a difficult phenomenon to study (not only because of what they do, and how such crimes are very dispiriting for the researcher ), because many of the checklists are for "ideal types". An ideal type is not implying what is 'morally ideal', it implies the traits that ideally fit into a theoretical framework; thus, some of the things on the checklists do not necessarily translate into a sociopath.
* For a thought experiment I will treat Jack as a real person, and discuss some aspects of her past and personality that people seem to be missing.
Some points from Jack's early childhood would suggest that she was very much loved by her mother, Jack was taken (according to the Broker dossier) at the age of 4 from her mother. At the age of four Jack would have been in the early stages of moral development (read Lawrence Kohlberg's work on moral developmental) it may also be true that Jack as a baby, was breastfed. This might seem menial, but the Oxytocin in a mothers breast-milk helps in 'pair bonding', and natural conditioning. Even though she had a horrid time with Cerberus, one cannot say that she never experienced love and closeness early in her life. Logically, if it is true that Jack had experienced a parental love early in her life, one cannot factor that out of her mentality.
She does express some kind of conditioned exhilaration from killing; though it must be stated that we all have an amygdala. It does not make it 'right', but we are trying to determine what makes someone a sociopath. Does such exhilaration make someone a sociopath, what are the psychological differences between Shepard getting a rush from killing in battle, and what Jack described ? One difference is that sociopaths maintains the creepy notion of making people suffer, much of the killing Jack talks about is not drawn out, but relates to her 'survivalist notions' and her idea of perpetual self-defense.
Sociopaths do not tacitly feel empathy, (they may understand the concept which is different) Jack shows empathy if you get to know her in ME2. Her entire persona seems to be built around some sort of 'survival notion', for Jack this involves, obfuscating many human emotions and her general feelings, her fear, sadness, and needs. She downplays her remorse and empathy then tries to showcase the absence of remorse and empathy. Perhaps this implies that, due to her time spent with criminals and assorted riff-Raff, she felt like she had to hide those things to 'survive among them', she then 'egocentrically' attributes her narrow view to the galaxy. She later feels comfortable enough to express those repressed feelings with Shepard, and by ME3 she is less repressive on herself, and has also accepted more 'societal-norms'.
*End of thought experiment*
It must also be stated, that narratively (in ME2) we witnessed Jack change overtime with Shepard, and we do not see Jack enough in ME3 (what is the total amount of time, 25 minutes at the most?) to say that she is 'totally fixed', because the games does not focus on her. Therefore, I think people are being fatuous when they say "I do not like how 'she is fixed' in ME3", how can people really know such a thing?
In summary, I would say that fiction does not present true sociopaths, it more or less represents the cartoon villain type stigmas,which some people seem to be infatuated with. Jack does not show a clear cut case of being a 'sociopath', she seemed to be more of a social isolate (bent on 'survival') and was hiding certain feelings and motives, until she felt like she could express herself to Shepard. I am not trying to say that sociopaths are innocent (don't get me wrong) but there is a misapprehension caused by the things people absorb from pop-culture, and what they do not take in from science. I think Jack was portrayed as a person who had a terrible time in her early life (i.e. Cerberus; she also became a criminal) who eventually has a paradigm shift away from crime and what have you, and into a new form of life.
* This ended up being a lot longer than I had anticipated.