Of course milk fans will focus solely on the part that says, "The doses of drugs were far too small to have an effect on anyone drinking them". Maybe if you only drink milk once in your lifetime... Just as smoking 1 cigarette won't kill you (if you're lucky, I guess), all those toxins in milk accumulate in your body and cause damage over time.
I don't think they can know that because there has never been a study done showing the effects of all of these chemicals mixed together on human health, they usually only test each one individually. The effects could be very bad. For a simple example: a study was done showing that if you smoke you will get lung cancer in 20 years and if you are exposed to asbestos, you will get lung cancer in 20 years, but if you are exposed to both, you will get lung cancer in 5 years. The risks go up exponentially. Plus how many other chemicals are in there that they just didn't test for? I remember a PBS Doco where Bill Moyers had himself tested for about 200 different toxic chemicals and he tested positive for all of them.