Yes, GMO is a refinement of crop modification techniques humans have employed throughout history. So the argument is that since those were "good", this can't be otherwise. But it's not that simple, a lot of the consequences of these modifications are at a closer inspection not that beningn. For example, the transition from hunter-gatherer cultures to agricultural ones came with severe detrimental impact on the health of those populations.
There is such a thing as something being more or less natural, that's why we have this concept. It's just that it's not easy at all to formalize. Maybe even impossible. But it won't go away, because it actually correlates to an essential aspect of reality.
you can however transplant genes across species, which just doesn't happen in nature. The fear that these improved crops would outcompete native grasses outside the farm wouldn't be unjustified if it weren't for Monsanto doing everything they can to prevent farmers from replanting their harvest.
Genes do spread without procreation. This is a certainty at this point.
And even when you do find someone who does they are making arguments like "the modified genes will break loose" ... which is absurd ... and that was a very smart individual, perhaps not where it comes to biology, but it's not like this requires much debt. (GMO is about transplanting genes, so any gene used has already "broken loose" before it is ever transplanted into any GMO crop).
"It's not natural". There is nothing behind that.