The concept of "defense mechanisms" is an interesting and complex one.

I'm suspect that CT's view will vary a bit from defense mechanism to defense mechanism. For example, Rachman and colleagues have done a bit of research into avoidance of affect. How does this apply to defense mechanisms? Well, suppose an individual relies on avoidance as their primary way of coping with anxiety. If they encounter an external stimulus that elicits anxiety, what will they do? They will try to avoid or escape that stimulus in order to avoid experiencing anxiety.

Well, suppose the individual encounters internal stimuli (i.e. thoughts, images, memories, ...) that elicit anxiety. It wouldn't be at all surprising if he or she avoided those thoughts/images/memories in one way or another. This could easily produce the behaviors that analysts interpret as revealing repression, reaction formation, and the like. Now, if what's actually going opn is avoidance behavior, this has clear treatment implications.

Other apparent defense mechanisms may work a bit differently. (More on that when I have a little more spare time.)