
I don't follow this logic. I can just as easily say, "Think of all the people who have been ill for a long time, they don't eat a high calorie/high fat diet but remain ill." By your logic that would mean that eating a high calorie/high fat diet would make them less ill.
Try replacing "exercise" in your statement with
anything else to see how the logic fails.
1. "Another way of looking at it is to think of all the people who have been ill for a long time, they don't participate in
religious services but remain ill." By your logic, we should conclude that going to religious services would cure ME.
2. "Another way of looking at it is to think of all the people who have been ill for a long time, they don't participate in
Japanese language classes but remain ill." By your logic, we should conclude that participating in Japanese language classes would cure ME.
3. "Another way of looking at it is to think of all the people who have been ill for a long time, they don't participate in
midnight headstands during the full moon but remain ill." By your logic, we should conclude that participating in midnight headstands during the full moon would cure ME.
See how it doesn't make sense?