When people act defensively, it's a self-protective mechanism with a clear message to the perceived intruder to "back off." The response seems aggressive, but the experience may be more instinctive, like pulling your hand back after touching a hot stove. The experience of pain triggers the self-protective response. So when we see this quality of defensiveness, chances are there's an emotional hot stove being touched underneath. The person may get this way because he/shealready knows this is something that isn't right for them and are already suffering from a guilty conscience about it.
When it comes to smoking, we have stigmatized it to the point where bona fide smoking addicts find it increasingly difficult to rationalize their smoking behavior. Instead they hunker down, and woe be to those who venture into this brittle territory. Of course, this quality of defensiveness applies to many other problematic behaviors such as alcohol abuse or overeating, as well as many other behaviors detrimental to our physical and mental health. One way to respond is to keep focused on getting healthy ourselves, and not try to control the other person through our own anxiety; to "detach with love." This doesn't mean we give up on the person, but it does mean we don't destroy the relationship to "save it." Readiness to change is the nice and neat concept sometimes offered to explain the stalemate. Yet even in the face of defensiveness, we can try to engage the person in a reasoned and cooperative way. It is, of course, reasonable to assert your legitimate interests in a situation by establishing ground rules or boundaries—for example, asking someone not to smoke in your house or around your children. Another example is not buying alcohol for an alcoholic, or drinking with someone when he or she becomes mean or dull. In the practice of psychotherapy, you can offer new perspectives on a problem many times, choosing words carefully and tactfully, and then suddenly the person has an aha! moment and shifts his or her own view of the situation. Another approach used by psychotherapists is to help the person get some distance from the problem by asking: "What if you saw someone you care about doing something detrimental to their health? What would you do?"