Why Are GM Crops Controversial?

Genetic modification (GM) of food and other agricultural crops holds out a lot of promises.  Unfortunately, it also inspires many worries.

The British public are especially skeptical after many food scares, that the scientists and corporate types who promote this stuff don't know what they're doing and may cause some kind of health (or other) disaster.  Genes interact with each other and the environment in ill-understood ways.

Dependence on GM crops may reduce biodiversity, promote super-weeds and reduce economic independence for small scale farmers.

Many environmentalists would also say that the problems that GM crops claim to address should be solved in other, less risky ways.
GM crops usually require the use of antibiotics (to turn genes off/on) in a world already over-dosed by antiBs.

Moreover, the promises are not clearly being lived up to.  Does GM greatly increase crop productiviity?  Well, no, not tremendously (not yet).  Does it lead to lower pesticide and fertiliser use?  Well not especially, not in the few studies done to date.  This may be for complicated reasons.  GM may foster the growing of crops in places previously thought to be unsuitable, but with the GM advantage and enough fertilisers/herbicides/pesticides, it now becomes possible to grow the crop there.

Does GM lead to food with a longer shelf-life?  Yes, but is that a good thing?