I wrote a paper about this not too long ago! I don’t know a lot about GMO’s, but I can answer your questions about genetic engineering in humans.
I feel that genetic engineering has a lot of promise, especially with eradicating genetic diseases, but it is still very new and research needs to be done with extreme caution. If gene editing technology was allowed to be used in more than just extreme circumstances, there would be a lot of room for misuse, things we can only imagine now, like changing someone’s physical features (eye color, skin color, etc). This is just one issue that could lead to less diversity and discrimination of a whole new kind, and just kind of spiral from there. There have been people who have died during experimental genetic engineering, I read a study where it was used to cure a handful of children of a genetic disorder, but then the tampering led to about half of them being diagnosed with a type of cancer that came directly from the gene editing, and at least one passed away. All this to say, genetic engineering can be a good thing, but there do need to be limits and further research should tread very lightly.
Kind of a long answer, sorry, but I hope this helps!