Cigarettes, DDT, Agent Orange, radium, hormone-leaching plastics, certain pharmaceuticals, antibiotic-laced meat. All were known to be harmful and were subject to a cover up to promote consumption.
DDT, Agent Orange, "hormone-leaching" plastics are not harmful to people. Antibiotics in meats are only a problem to a small number of allergic people. Of course, if you are really a vegetable or insect, then I could see why you consider the first two to be threats.
That is, in fact, what he's saying, although it wasn't definitively shown. But clearly it was known to be a carcinogen when they built my high school in the early 70's, and yet they were still using it as a standard insulation and fireproofing material. I have lots of asbestos tape in my house, too.
Lead paint, though - there's a good one. Everybody knew you shouldn't drink it, but nobody suspected the dust was a problem. (Although Japan had already banned it by the 20's, if I recall correctly, while America was still merrily painting everything in sight with toxins).
And of course, the Romans didn't even know you shouldn't drink it. Although the benefits lead plumbing in Rome due to widespread availability of clean water almost certainly outweighed the costs of some stupider Romans.
There are like 100 forms of asbestos with 6 types being extremely harmful. The manufactures started using the cheapest of the materials (which are extremely difficult to tell apart).
http://en.wikipedia.org/wiki/Asbestos#History_of_health_conc...