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.

I use the furniture of espionage to amuse the reader, to make the reader listen to me, because most people like to read about intrigue and spies. I hope to provide a metaphor for the average reader's daily life. Most of us live in a slightly conspiratorial relationship with our employer and perhaps with our marriage. I think what gives my works whatever universality they have is that they use the metaphysical secret world to describe some realities of the overt world.
--John le Carré, as quoted in "Master of the Secret World: John le Carré on Deception, Storytelling and American Hubris" by Andrew Ross, in Salon (21 October 1996); also in Conversations with John le Carré (2004) edited by Matthew Joseph Bruccoli and Judith Baughman, p. 141

Describing Smiley as a sociopath--as someone who doesn't have the conscience that normal humans have--sends precisely the opposite message.