Sources on the safety claims? Plastics were more flexible (in terms of usage), cheaper, and reduced use of paper and wood which, at the time, was a major concern as companies were clear cutting forests. Today, forestries follow sustainable practices. And while plastics are convenient (and in some cases a major benefit), there are plenty of areas where paper and other plant based products would still be just fine and worth it to reduce the harm that we now know plastics cause.