The sinister overtones that many hear in the phrase "behavior modification" arise from the perception that it necessarily describes the coldly clinical manipulation of one creature by another. The efficacy of classical and operant conditioning rests on our ability to generate involuntary responses to selected stimuli, a process that appears suspiciously like brainwashing. If someone acquires the power to circumvent my conscious intent, to play upon my more or less submerged desires without my reason's consent, what am I but a puppet?
It's no real consolation to observe that, under the scrutiny of neuroscientists, the whole phenomenon of willed action begins to appear less and less substantial and may prove no more than a sustained delusion: it's a necessary delusion, indispensable to our sense of mental coherence. The related delusion that we might more productively dispense with is the conviction that reason rules (or should rule) our behavior. It leads us to assume that we should seek change in ourselves and others through the careful application of logic, when the truth of our experience (and increasingly of scientific study) is that emotions have infinitely more suasive power than reasons do. Or, as Pascal noted, the heart has its own reasons, to which reason must give sway.
Maybe the general mistrust of behaviorism actually speaks to an intuition in this direction and a general anxiety around the mixing of "cold" logic with "warm" feeling: someone with the power to stimulate my most primal emotions (joy, fear, desire, disgust, etc.) may well abuse it if he regards me through the lens of reason as a mere object for the accomplishment of his ends.
This is jumbled and something I need to work through at much greater length (you see my faith in reason perseveres!), but I do know that my emotional entanglement with my training "subjects" is the sine qua non of my use of behaviorist methods.
Not that emotional entanglement is any guarantor of virtuous ends. (The Manchurian Candidate supplies a case in point.) Sigh. I'll have to try to catch this tiger by a different toe.