If you'd try eating real pure non-gmo'd banana you'd break your teeth because of all the seeds, but that thing hasn't existed for millenia. Apples would be disgusting too by today's standards.
The slow change in dogs or crops over many decades or generations is tolerable. But rapid change can kill, or at least it excites danger signals in the affected organisms (people).
A car that creeps towards you slowly is fine. One that moves too fast might kill you.
I think rate is the central question in this problem, but it always gets elided in discussion with the word "just," as if rate was a minor concern.
Compared to that widespread action, GMO is safe as it is thoroughly tested. Though diversity is not being increased with it either.