* We are often creating chemicals that do the job of existing chemicals safer and more efficient. This ban would probably include a grandfather clause for old chemicals, and thus we might be using inferior products and doing more harm than we otherwise could. Look at refrigerants as an example of a chemical compound that has improved over the decades.
* Many chemical compounds introduced in the last 100 years directly improve productivity. The United States is in economic competition with other regions of the world. We could be creating a disadvantage that reduces our geo-political power.
* Many of these chemical compound increase quality of life. There's a strong unitarian argument for sucralose and polyurethane insulation.