I'll start off by saying I agree with your point of view, but I've also looked into the opposing side so I'll write up their arguments here and see if you think any of that is useful. Most comes from a misunderstanding of science, misreporting of facts and general paranoia about the "evil monsanto" boogeyman and exploitation. This is going to be long, so apologies.

The first issue is the narrow effect of GM traits. The majority of GM crops express Glyphosate resistance, with the second highest being Glufosinate. Similarly to using antibiotics in animal production this selects for weeds which have resistance to these genes. There are several hundred identified species of weed that have developed Glyphosate resistance with many more expected to exist but haven't been catalogued yet. This is similar to insect resistant (BT toxin expressing) plants, with widespread usage of a specific BT toxin strain potentially resulting in BT resistant insects - again this has been seen in the pink bollworm.

Now we move onto the issues surrounding the herbicides themselves. Many environmental organizations are against herbicides on principle believing that organic farming is somehow sufficient to feed the entire world's population. Greenpeace for example have linked Glyphosate usage to birth defects, carcinogencity, increased disease and toxicity to soil bacteria and animals. You can read about that here.

Similarly they have attempted to link health issues with the BT toxin. A study has shown potential accumulation of the toxin in the blood, and another suggested haemotoxicity in rats after being fed BT crystals in varying concentrations. Another issue with BT comes from potential targeting of non-target species. You may remember in the early 2000s there was some controversy over GM crops and the Monarch butterfly - this was found to be inaccurate however BT crops did target the black swallowtail butterfly despite it not being a pest species.

Now we can talk about issues with the specific technologies. Many plant transformations are done with Agrobacterium-mediated transformation, which inserts DNA in a semi-random manner into the plant genome. Anti-GMO organizations believe this may produce unknown new toxins which may harm people eating the crops. Newer technologies (e.g. ZFNs, TALENs and CRISPR) are able to transform far more precisely but the environmentalists are still against using these for whatever reason. Similarly to this you will often hear about allergenicity of new GM strains, based on a protein conferring weevil resistance in a transgenic pea. The protein was originally isolated from a bean plant and showed slightly different conformation in the pea resulting in significant allergic responses in rats.

Another issue with the technologies is the necessity of selectable marker genes (often an antibiotic resistant gene in the plant) which is used to select for resistant strains during genetic transformation. People think that these resistant sequences may transfer to gut bacteria or other organisms via horizontal transfer and create dangerous pathogens. Due to this markers tend to be antibiotics that are no longer commonly used in medicine (e.g. kanamycin). Additionally newer transformation technologies can remove the resistant marker gene if desired.

Most of the arguments against them on Reddit are about "big agro" and monsanto. Since GMOs make up a large proportion of crops in the USA some have complained of a lack of choice between GM and traditional varieties, forcing them to plant GM against their will (90% of soybean grown in the USA have traits developed by Monsanto). This also leads to concerns around monopolies and price fixing by the large corporations - seed prices and farming costs have been slowly rising. Similarly consumers may wish to not eat GMOs due to believing the health concerns or on principle, and as so much food grown in the USA is GM they have trouble avoiding it.

GM companies also have a lot of power in the US government, lobbying officials, and several positions in regulatory organizations are held by ex-monsanto employees potentially representing conflicts of interest. Something else you may hear about is Monsanto suing farmers growing unlicensed GM crops which have found their way into their fields "accidentally". In reality this is solely due to farmers saving seeds against the terms of use and no farmers have been sued for accidental cross-contamination.

Finally there are potential exploitation issues in developing countries such as India. BT cotton is being rapidly adopted there but often fails due to drought. This has been linked to increased farmer suicides due to them going out of business. Additionally some knock-off GM crops which do not offer full resistance have been sold there resulting in crop failure. This has led to a ban on GM crops in some regions in India.