The drug then gets into the milk and if you have a penicillin allergy you become very ill from drinking the milk. It was not the milk or anything used to preserve it that made you ill, rather the drug that was used to treat the cow. Even though in most cases food additives are very safe, we still must use our heads when using them. There are certain contitions that would prevent us from using certain things. For example, a person with high blood presure or heart disease would have to watch their sodium intake.
Many people have allergies to certain food dyes.
Does this mean that these dyes should be taken off the market. Of course not, this only affects a small percentage of people and is totally harmless to the many other millions of people. Then there are the people who have a tendency to store up too much iron. This is a disease which is known as hemochromatosis. They would, however be perfectly alright for the rest of the population, and in many cases very benifitial.