Genetically Modified Organisms

Genetically modified organisms pose unknown risks because ...

... genetically engineered bacteria or plants may transfer manipulated genes to other species in an ecosystem. The risk of a negative impact on the environment is unknown.

... genetically engineered organisms may produce toxins or allergens harmful to other organisms.

... safety and risk assessment is not provided by independent (government) agencies but by the parties producing the genetically modified organisms (the problem of self-policing).

... the potential existence of superweeds that would dominate and destabilize ecosystems and accelerate the loss of biodiversity (endangered species).

Read more about this risk-discussion here.