Christ is enough for everyone, end of story.
However, it can sometimes be difficult to witness to, teach, and correct people with certain mood/personality disorders such as NPO, BPD, etc. Specifically those that are unable to feel empathy or introspection.
A negative and positive anecdote I know of from people who displayed sociopathic tendencies:
My grandparents (I believe) have NPO (Narcissistic Personality Disorder). They raised me, and I know I am mentally and emotionally unable to love them and show them the gospel well, so I do not speak with them. Many agree with this, and many don't.
Before my husband was radically changed by the gospel, he was very manipulative. We wouldn't say he was a narcissist, but he certainly wasn't a very good friend. Christ quickly and radically changed his heart, and he is an entirely different person.
If I were to believe that a sociopath could not be changed by Christ, it would diminish what Christ did, and it would deny that my husband has changed. The bottom line is, we don't get to choose who is and isn't saved. We only get to show the gospel and watch as lives are - or aren't - transformed by Christ.