The author doesn't need to consider that "some food additives are harmful to most people." We are talking about Yellow Dye No. 5 specifically, which we already know might cause allergic reactions in a few consumers. The author factors this potential harm into the conclusion that the dye should not be banned. The dye could be harmful to a few people, not to most people, so C is not relevant.
The real problem is that the author has misinterpreted the principle. Health-related benefits should weighed against potential risks. If the health benefits of Yellow Dye No. 5 outweighed the allergy risk, then it should not be banned, and the conclusion would be properly drawn. However, the author only discusses "enjoyment of the beverage," which is not a health-related benefit. This flaw is best expressed by B.