One of the problems with Monsanto, besides being a near monopoly, is that through encouraging the use of Roundup ready seeds, they are encouraging farmers to continue the practice of polluting our soils with that herbicide. I live in a rural community and have talked to farmers about why they need to use Roundup when for centuries they did not. It turns out that the weed crops steal water and nutrients and also make it more difficult to harvest their crops. Weeds tend to screw up their harvesters. It is not necessarily to increase yield.
Personally, the main thing I have against GMO crops is that as a consumer, we are not told if what we are eating is a GMO crop. Most of the crops we are talking about in my area are used for animal feed (poultry), and not necessarily going for direct human consumption. As GMO seeds become more prevalent, however, direct human consumption of these crops will be unavoidable. Many countries have banned their use, of course the US, being corporate driven, has not.
Monsanto does produce a Bt GMO seed that is in sweet corn that that kills insects. Bt is a natural insecticide, but I don't want to be eating it, and I don't want it killing beneficial insects either. Fortunately, I grow enough corn to meet my needs. Others do not have that luxury. Plus, who knows what other produce is full of Bt and other insecticides.
Using Monsanto seeds also is limiting biodiversity of crops, something organic farmers and seed savers are trying to maintain.
As for those who think Roundup is harmless, you should come see my vegetable garden after the farm behind my house is sprayed with roundup and all the bees in my garden are dead as doornails, still sitting on the flowers I planted to attract pollinators.
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