The stimulus starts by commenting on a phenomenon: long-term cigarette smoking leads to health problems like lung disease and cancer, and this is a "scientifically well-established fact." However, the stimulus then argues against a belief many people apparently hold, stating that one doesn't have to deny this fact to reject the idea that tobacco companies should be held responsible for smokers' health problems. In other words, you can agree that this fact is true and still think that tobacco companies shouldn't be held responsible.

The author backs up this claim with an analogy: it is "undeniable" that eating too much candy can cause health problems like tooth decay, but no one thinks candy eaters should be able to sue candy companies over those health problems.

The argument rests on an analogy between eating candy and smoking. Any analogy presupposes that the things being compared are actually comparable — in other words, that there are no relevant differences between the two things that would undermine the analogy.

But in this case, even though eating too much candy and smoking cigarettes long-term both lead to health problems, it seems like there could be some relevant differences between the two activities and the health problems they cause. For instance, eating candy might not be as addictive as smoking cigarettes, and the health problems from eating candy — like the "cavities" the stimulus mentions — might be less serious than health problems from smoking.