I think you should separate and distinguish between several things in order to have a meaningful discussion.
The first and main one: Monsanto does not equal GMO and GMO doesn't equal Monsanto.
Monsanto is a corporation that uses irresponsible GMO and horrible and manipulative business practices to make money.
It doesn't mean that all GMO will always be used in that way, you CAN use this tool responsibly and for a lot of good.
Just because Monsanto doesn't, doesn't mean you can NEVER do it.
If you are not able to understand this point, this discussion turns into an emotional exchange of words and means nothing.
Just like the fact a terrorist can use explosives to blow up a school, but it doesn't mean that explosives themselves are a bad thing, when used for mining or demolition for example.
Secondly what is the difference between selective breeding and GMO techniques?
In nature different species evolve over millions of years. You wrote "Try crossing a tomato with a turnip in your garden and see what happens. Nothing."
The fact you even HAVE a tomato and a turnip on this planet means there used to be a plant which was a common ancestor for these two species and through the process of evolution they diverged into the different species we know today.
Selective breeding IS a form of genetic manipulation that relies on the same basic random processes that evolution relies on, but it is guided
by humans, who favor certain phenotypes. However is takes several generations and lot of resources.
If you compare the DNA of a Chihuahua to that of a wolf, you will see many differences that would have never happened in nature either.
These modifications may have happened by chance, but were incrementally and artificially propagated by us, and not by natural selection, which is how evolution works.
It is not a natural process.
GMO on the other has nothing to do with crossing species. You inaccurately describe genetic modification as "Genetic Modification is removing snippets of DNA in the genes and replacing those snippets with a something totally unrelated to that plant or animal species and could never happen in nature."
Do you know how genetic engineering in plants was done (and actually still done in most places) in the pre-CRISPR era?
Using an organism that exists in nature and is called Agrobacterium. This bacteria is responsible to horizontal genetic transfer between individual plants, and also between different species of plants, for example, a tomato and a turnip.
In fact, this bacteria and several plant viruses are probably responsible for the emergence of many plant species as we know them today, as part of evolution, by moving around random pieces of DNA between unrelated plants.
The difference is that in the lab, we can decide which genetic sequences will be transferred to the plant.
The snippets we are introducing the lab are not random, they are genes we choose carefully and after a lot of thought, because they are known to infer a certain phenotype that we deem favorable, just like in selective breeding. For example, sometimes a single gene, which makes a single protein, can infer a resistance to a certain pest, that will otherwise require harmful pesticides to deal with. You decide which option is less harmful.
So it is taking a naturally occurring substance, and using it in a new context.
Just like people used to chew tree bark to get acetyl salicylic acid, and now we can make it in a tablet and it saves thousands of lives and costs cents (Aspirin).
This doesn't mean there aren't any problems with the process.
I believe those plants should be tested very carefully before introducing them into an ecosystem, and before approving them for animal or human consumption.
This part is not done today and I think it is very irresponsible, and should be illegal.
Saying that all GMO is automatically and fundamentally good, is just as ignorant as saying that it is bad.
It's not about the tool, it's about how you use it.
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