I always assumed that the Union of Concerned Scientists, a special interest group, spoke for my interests as a scientist. They definitely do not.
Science had a brief history of UCS a few months ago. This group originally focused on what they considered to be an "appropriate" level of regulation for nuclear power. Since, they appear to have consistently leaned less towards the scientific viewpoint, than the environmentalist one (in the worst, religious fanatic sense of the word). I was incensed to discover on their website that they opposed genetic engineering for the same silly reasons offered elsewhere.
Well, they're at it again. They recently released the report: Failure to Yield: Evaluating the Performance of Genetically Modified Crops. According to a story in Nature Biotechnology, contacted public-sector crop scientists have been "uniformly critical" of this report, for lots of good reasons described therein.
I'll keep it simple. They suggest that Bt crops don't have higher yield than their conventional versions. (Bt is a natural bacterial toxin that kills insects and is often used in organic agriculture. Bt-GMO crops have been genetically engineered to produce the protein themselves instead of relying on the farmer to spray it.)
This is a complete strawman argument. The whole point of having the crop make its own Bt is that it saves the farmer money, time, pesticide applications and tractor fuel. This is good for the farmer and the environment, whether yields are higher than with conventional crops or not. And let's not forget that not all pesticides are created equal. The active ingredient in Roundup (glyphosate) is less dangerous to humans than either caffeine or aspirin. Additionally, GM glyphosate and GM Bt resistance have largely supplanted the use of infamously dangerous old-fashioned pesticides like atrazine and organophosphates. Whatever threats you may hypothesize to the former two, the latter two have left a real record of human death and ecological destruction.
Farmer's aren't stupid. If Bt crops didn't work, they wouldn't have been adopted at such a phenomenal rate.