To be fair, GMOs can just as easily be unsafe; the difference in that regard is that with GMOs there are fewer ways things might go wrong, and they're much more easily enumerated and examined.
The best example of an "unsafe GMO" would be this: https://pubmed.ncbi.nlm.nih.gov/8594427/ (brazil nut proteins were transferred to soybeans; the proteins happened to be ones that cause brazil nut allergy. If this had been rolled out in large scale, probably some fraction of consumers would die).