While it appears that the main reason for not supporting scientists as advocates is that scientists have a narrow field of expertise, in reality this does not matter whether it is true or not. It is true that someone who practices entomology would not be appropriate to advise on matters of the earth's crust and geological evolution, that is why there are geologists. There are a multitude of different fields that a scientist can belong to and just as many scientists filling these positions. When developing an ecological survey or an environmental impact assessment it is important to realize that there isn't just one scientist being consulted. There are teams of scientists, each involved in different yet indisputably connected fields. The idea of conducting scientific activities or engaging in policy without recommendations from the very people who determine what conservation biology is, or how to go about accomplishing it, is as flawed as NASA trying to reach the moon without consulting physicists or rocket scientists to determine the necessary propulsion and aerodynamics to achieve escape velocity. Even with all the brilliant minds in NASA, there were dozens of disasters along the way before success was eventually realized. Why? Because it was a learning process. Just because one advocate disrupts a single project is not a reason to scrap the development or change the process. “Environmental policies and actions can be improved when environmental scientists engage in science-based advocacy, by calling attention to relevant scientific information and ensuring that policies and their implementation are consistent with the best available science.” (J. Meyer et al) Of course counter measures need to be considered to prevent corruption and stagnation, but what aspect of human life style doesn't involve these dangers. Too often our society overreacts to the latest disaster or media hyped horror story when the correct response is to analyze the situation, discover where the breakdowns in communication occurred and learn from the entire process. More importantly is the realization that advocates are just one cog in the formation of policy and decision making. Advocates do not implement policy, approve it, ultimately determine its true nature or enforce it. There are many individual parties involved with producing an effective policy. Regardless if scientists are allowed to be advocates for the very research they produced or not there will be advocates present who are against their studies. Using third party participants or word-of-mouth advocates is akin to using a puppet with strings attached, it looks harmless but you don't know whose holding the strings. It is the responsibility of the policy making body to surround themselves with the correct individuals to advocate, both for and against, developments. Having a healthy mix of pro and con advocates is important in evolving policy and removing scientists from the equation just reduces the effectiveness of this give and take.
Judy L Meyer, Peter C Frumhoff, Steven P Hamburg, and Carlos de la Rosa 2010. Above the din but in the fray: environmental scientists as effective advocates. Frontiers in Ecology and the Environment 8: 299–305. http://dx.doi.org/10.1890/090143