The danger is that unsubstantiated opinions, stated often enough, will be mistaken for facts. A study can be designed to produce almost any desired result, but such studies are by definition not science. The nature of scientific inquiry itself can be frustrating because it is human nature to want immediate and permanent answers to questions. Especially in the environmental sciences, answers may be long in coming. It is far easier to conduct controlled experiments in a laboratory than in nature.
Effects often take many years to become measurable.
Even then, the causes can be very hard to pinpoint. Uncertainty is a natural part of science that doesn't translate well to public policy decisions. Still, the better we understand how science works, the better informed our decisions will be. Each problem or question requires a different approach. However, certain methods are basic to science.