Some scientific knowledge indicates that there is no safe level of exposure to a cancer-causing agent. In theory, even one molecule of such a substance has the potential for causing cancer. Section 112 of the Clean Air Act requires that all cancer-causing substances be regulated to ensure a margin of safety. Some environmental groups have argued that all emissions of such substances must be eliminated to attain such a margin of safety. Total elimination would likely shut down many major U.S. industries. Should the Environmental Protection Agency totally forbid all emissions of cancer-causing chemicals? Discuss.