It depends upon how unstable your knee is. Some ACL patients can control the instability produced by the ligament rupture with strong muscles and excellent proprioception. ACL bracing can sometimes help reduce the incidence of instability episodes. But, any brace placed on the outside of the skin, cannot control the movement of the bones completely, so all braces can be overcome.
Can you hurt the joint worse, YES. With every episode of instability, the articular cartilage is damaged a little. In some cases, large pieces of the articular cartilage can be knocked off. Treatment of articular cartilage defects is very difficult and not very satisfying.
The reason to fix an unstable knee is to try to reduce the chances of the knee going on to significant arthritis as the years pass. Even just a little wobble, not very noticeable to the patient, can have significant consequences in terms of producing traumatic arthritis.
So, it depends upon how unstable your knee is. But, you can do more damage to the knee.