Wesleyan theologian, John Drury, once defined heresy as "substituting part of the truth for the whole." He went on to say, "this is why heretics are not completely wrong and often have much truth to share. The problem with heresy is not its utter falsity, but its one-sidenesses."
I believe the Drulogian is right on target here . . . and the funny thing is, the harsh, rigid, narrow folks who are most likely to call others "heretics" are, by this definition, heretics themselves!