GMO covers a lot of ground (literally and figuratively). GMO just means its genetic code has been tampered with. The question is how and for what purpose. An infinite variety of modifications could be done and a wide variety have been done, including creating glow in the dark cats that have had a phosphorescence gene inserted and inserting anti freeze genes from Antarctic fish into tomatoes to make them more frost resistant.
As you say, one of the commonest modifications is "Round-up ready," making the plant resistant to Round-up, so the fields can be sprayed with it instead of weeding. The problem with that is not the modifying, it is the spraying. Round up has lots more environmental impacts than was first understood, e.g. :
Glyphosate, the active ingredient in Roundup, is acutely toxic to fish and birds and can kill beneficial insects and soil organisms that maintain ecological balance.
Glyphosate is the third most commonly-reported cause of pesticide illness among agricultural workers in California.
The surfactant ingredient in Roundup is more acutely toxic than glyphosate itself and the combination of the two is yet more toxic.
https://www.ecologycenter.org/factsheets/roundup.html
Another significant problem with the wide spread use of Round up ready GMOs and therefore routine spraying of Round-up over square miles of crops, is that more and more weeds are now becoming Round-up resistant. By over-using/ abusing the tool, they are rendering it worthless.
he area of U.S. cropland infested with glyphosate-resistant weeds has expanded to 61.2 million acres in 2012, according to a survey conducted by Stratus Agri-Marketing. Nearly half of all U.S. farmers interviewed reported that glyphosate-resistant weeds were present on their farm in 2012, up from 34% of farmers in 2011. The survey also indicates that the rate at which glyphosate-resistant weeds are spreading is gaining momentum; increasing 25% in 2011 and 51% in 2012.
https://www.cornucopia.org/2013/02/glyph ... ore-farms/
Did you get that from 34% to "nearly half" in ONE YEAR? !!
A similar phenomenon is occurring with GMOs that have genes inserted to produce Bt (bacillus thuringiensis). Bt has been beloved of organic gardeners, because it is a bacterium that infects various kinds of crop chewing caterpillars/ worms, but nothing else and causes no environmental harm. Used selectively, in small areas of outbreaks, we might have used it forever. But now that Bt is being inserted in to everything and blanketing square miles of monoculture crops that produce the Bt toxin in every cell, we are also breeding Bt resistant pests, such as:
corn rootworms
https://www.sourcewatch.org/index.php?ti ... nt_Insects
cotton bollworms
Daniel Stolte, "GM crop trouble as pests adapt," Western Farm Press, June 21, 2012.
and a number of others.
So the problem isn't the simple fact that something is GMO, but what particular kind of modification for what purpose and what are the impacts of that modification.
What I hate is that consumers have no way to know when they are purchasing GMO organisms / products, so no choice and no way to vote with their dollars for whether they want that modification. I believe GM organisms and the products containing them should have to be labelled as such, so that consumers can at least exercise some choice.