Surely the thousands of years of human civilizations consuming non-GMO products should count as a fairly strict approval process?

A vast majority of what you eat has been developed, not thousands of years ago, but some years or decades ago, using processes such as induced mutagenesis and selection. The variance in genome produced by GMO technology is very small compared to the changes in developed plants, which is not researched at all prior to feeding to humans.

For example, the Honeycrisp apple was created in 1960, not thousands of years ago. Incidentally, it was also patented (in 1988, expired in 2008).

https://en.wikipedia.org/wiki/Honeycrisp