Do you think that if a lesion has a 100% chance to cause you to decide to smoke, and you do not decide to smoke, you might have the lesion anyway?
No. But the counterfactual probability of having the lesion given that you smoke is identical to the counterfactual probability given that you don't smoke. This follows directly from the meaning of counterfactual, and you claimed to know what they are. Are you just arguing against the idea of counterfactual probability playing a role in decisions?
"Counterfactual probability", in the way you mean it here, should not play a role in decisions where your decision is an effect of something else without taking that thing into account.
In other words, the counterfactual you are talking about is this: "If I could change the decision without the lesion changing, the probability of having the lesion is the same."
That's true, but entirely irrelevant to any reasonable decision, because the decision cannot be different without the lesion being different.
You're given the option to torture everyone in the universe, or inflict a dust speck on everyone in the universe. Either you are the only one in the universe, or there are 3^^^3 perfect copies of you (far enough apart that you will never meet.) In the latter case, all copies of you are chosen, and all make the same choice. (Edit: if they choose specks, each person gets one dust speck. This was not meant to be ambiguous.)
As it happens, a perfect and truthful predictor has declared that you will choose torture iff you are alone.
What do you do?
How does your answer change if the predictor made the copies of you conditional on their prediction?
How does your answer change if, in addition to that, you're told you are the original?