Much of the Left-wing opposition to GMO is more of an environmental thing.
True.
We know from a lot of experience that introduced evasive species are detrimental to the environment and devastating to the ecology of the area the organism is released into. This is complicated and exacerbated when that organism has no natural predators.
Many ecologists are shifting on this. There are a couple examples of invasive species that cause a lot of damage, but most invasive species don't, or only cause short term damage. Regardless, domesticated crops will not become invasive species. Farming would be extremely simple, instead of hard, if that were the case.
If we introduce a glyphosate resistance crop to an area and there is cross pollination with other plants, especially weed species, we could end up with glyphosate resistant weeds.
Sure. There are 42 glyphosate resistant weeds. That is not a good thing. But what about the 452 cases of weeds being resistant to other herbicides created through non-GMO methods? Last I checked 452 is more than 42? Things like EMS mutagenesis - much riskier and a tiny fraction of the regulations - which long predates GMOs and is something that the environmental movement says nothing about because they are simply anti-science and understand that their followers are completely ignorant about agriculture, know nothing about plants, and don't care that if GMOs were made illegal tomorrow 100% of herbicide resistant GMOs would be replaced with herbicide resistant non-GMOs (and the creation of glyphosate resistant plants predates GMOs too).
We might also see glyphosate resistant weeds simply because as we kill off all of the ones that aren't, we only have those ones left, kind of like the super bug issues. And in fact we are seeing this with hundreds of reports around the world about the increasing nature of glyphosate resistant plants, in particular Perennial Ryegrass, Kochia, and a number of the members of the Amaranthaceae family.
You know a lot about glyphosate resistant weeds, but nothing about all the resistant weeds to other herbicides. Why do you think that is? And what do you think the financial incentives are for certain groups to loudy focus on one issue and ignore the others?
Herbicide resistant crops are going to continue to be a thing. Farmers are not going to go back to having a ton of kids so they can spend the whole summer weeding fields. Consumers are not going to agree to pay the ridiculous cost increases that would be required for farms to employ even the cheapest labour to do that either. The solution was (and is) crops that are resistant to multiple herbicides acting on multiple different sites rotated with other crops that are resistant to other herbicides acting on different sites. This should have been a requirement from the get go, but activist groups vocally opposed this commonsense solution. While this can be done with older non-GMO methods, GMO would be much better, and CRISPR in turn will be much better, which is why countries that have been very anti-GMO are not classifying CRISPR as GMO - which requires amazing acrobats, but nations understand that how incredibly stupid they were to accede to the anti-science of the anti-GMO groups and won't make the same mistake again, but at the same time won't do the commonsense action of changing directions on GMOs because they understand that their populations have been made unredeemably stupid by the anti-GMO groups.
There is also a valid concern that making crops, such as corn, canola, soy, and others, glyphosate resistant leads to farmers using it more often on the food crops that we then consume, and that this means we are consuming more of these herbicides in our food, and thus suffering for health related issues that have been linked to them.
Again, you have been sold conspiracy theories by ideological activist groups that are financially dependent on selling you those stories.
These are highly valid concerns associated with GMO's,
They are both not highly valid concerns, nor are the concerns a GMO issue. Again, you are just a sucker for conspiracy theories.
and ones that we shouldn't just handwave off as pseudoscience or scare-mongering because there is real evidence of their effects on us and our environment.
We should call it what it is: pseudoscience and scare-mongering, created by Andrew Wakefield level kooks, such as Vandana Shiva and the Maharishi cult, and sold to ideologically agreeable people who don't know enough to even evaluate the lies they are being fed.