First of all, you are correct. We do not teach that the types only go to the healthy (or "high side") of their Direction of Integration, nor do we teach that we only go to the unhealthy (or "low side") of our Direction of Disintegration. We have not taught anything even remotely like that for many years. But this question has been raised repeatedly, so we want to say a thing or two that might simplify our views on the Directions.
With regard to the Direction of Disintegration, we feel that, under increased stress, a person goes to the type in his or her Direction of Disintegration at roughly the same Level as his or her basic type. We have explained this in the Revised Edition of Personality Types, and have included descriptions of what happens with the move to the Direction of Disintegration for each type Level by Level. Seen in this way, the move in the Direction of Disintegration is neither "up" or "down," but lateral. Thus it is neither to the "high side" nor to the "low side" unless the person is already at the "high side" or "low side" of their own type.
We see the Direction of Disintegration as a way of relieving stress by acting out behaviors that are not native to our type. It functions as a "safety valve" so that potentially overwhelming pressures and anxieties within the psyche can be let out. We feel that the Direction of Disintegration is not "bad," and can even be adaptive. It helps to slow the descent to a lower Level of our own type—a much more serious problem. In a certain sense, it is like a hasty lateral pass by a football quarterback who is being rushed by the defensive line: better to take a risk than to be sacked for sure and lose yardage. But in the case of our personalities, this move is usually unconscious and compulsive, and seldom resolves our problems. In certain circumstances, it can even make them worse. Also, by our definition, the move in the Direction of Disintegration (to the "stress point") comes into play at Level 4 or lower. In other words, "acting out" due to stress, occurs in the average to unhealthy ranges of our type.
By contrast, the Direction of Integration describes the process of consciously integrating new aspects of our Being that begins to come into play in the healthy Levels of our type, although we can first detect it around Level 4. The Direction of Integration represents a conscious movement toward wholeness. (For this reason, Level 4 is critical in that it marks a choice point—a stage at which we are more receptive to transformative energies. At Level 5 and lower, it is harder for us to respond to these energies: our personality is more dense and defended.)