Mitt Romney wants to open up more federal lands and waters to drilling for oil and natural gas. His party is pushing, in the name of freedom and economic opportunity, to roll back a variety of environmental protections. Republicans, including U.S. Senator Pat Roberts of Kansas, are seeking to ease pesticide regulations; some are even questioning the Environmental Protection Agency’s ban on DDT, reopening a controversy that stretches back half a century. Fifty years ago this month, Rachel Carson published “Silent Spring.” This critique of the America’s dependence on chemical pesticides is widely hailed as one of the most influential books of the twentieth century.