I don't think Smiley's a sociopath at all. One of le Carré's main themes (in all his work) is that ordinary people do unspeakable things and heroic things in certain circumstances, and that spies aren't fundamentally different from the rest of us.

Having just 'read' the audiobook, I agree with this reading (and I'm looking forward to seeing the movie, although I think I'm also gonna be wishing for subtitles!).