"Why are they opposed to even GMO field trials?"
Let me explain what happens in a crop's field trial, by comparing it to human measures.
Suppose you take a patient who's infected with the AIDS virus, and inject him with a recently developed experimental medicine that you CLAIM will cure him. Now to test this, imagine taking his blood and semen samples, multiplying them and injecting 10,000 regular civilians with them.
Imagine not informing those 10,000 civilians about it and letting them go about their business - for several years.
And then after a whole new generation has been born, suppose we can only NOW, after a long term, really measure whether the medicine was actually effective or not.
If it turned out to be effective, then FINE, no damage. Yay.
But what if it didn't? Then by the time this comes to light, those 10,000 people will have spread the un-cured AIDS virus it to their partners and further on to the children that they concieve.
Would you be able to contain the outbreak you caused while experimenting?
This sounds freakishly mad-science, doesn't it? Well, now do some replacements:
Replace all the people with individual brinjal plants, and the initial test patient with a BT-Brinjal plant.
This is how plants procreate. Each plant makes and releases thousands of pollen, and the wind and the bees and flies and birds and animals and occasionally humans take them at random to other brinjal plants in the vicinity. Pollination happens, and then the next generation, the seed, is formed.
One field growing an experimental batch of BT Brinjal, will, within one harvest, spread its pollen to neighbouring fields, and get into their gene pool by the next season. When it comes to field trials with plants, there's no such thing as inoculation, there is no such thing as control.
BT Cotton... was released without telling anybody and has spread across the country. The "field trial" that Monsanto started without bothering to ask anybody's permission, has now mixed in with the mainstream in the way I described above. Whether there are harmful effects or not -- was it really upto Monsanto to play with our eco-system without telling us about it? At least we're not eating the cotton. But many animals are. These organisations - Monsanto or the government - aren't doing any monitoring. It's still too early to tell about any long term effects. It's something we all have to live with now.
But even keeping potential health effects aside, there's the economic angle. The GM seeds' DNA have been patented by Monsanto. Any crop sample you take, a simple DNA test will reveal if it's got Monsanto's GM strain or not. And Monsanto has no intentions whatsoever to open-source their seeds' DNA. Look up the suits it's filed against family farms in the US for growing GM Soy without paying Monsanto any royalties. Those farmers didn't steal anything : the GM strains entered their crops' gene pool by natural cross-pollination from neighboring fields that were growing GM Soy. Even if it's out of their control, their government is forcing them to pay Monsanto. This is pure profiteering.
So it's a loss of food sovereignty - switching over to GM practically means of all the money farmers make, a part will go to Monsanto. Already they've been increasing the price of their BT Cotton seed they sell to farmers - one major factor driving the farmer suicide rate in our country at 1 every 30 minutes. Something that used to be freely available and abundant, is now owned by a foreign company.
This makes it in the best interests of Monsanto to SPREAD their GM varieties. And just starting field "trials" will do the trick.