The first case depends on the sterilization method: If plants produce no pollen, that is one thing, but sterile GMO pollen will prevent reproduction in neighboring non-GMO plants it "fertilizes." Proving that requires no experimentation beyond Mendels existing ones.

Likewise, if GMOs are hardier than non-GMOs, natural selection makes their dominance inevitable, as environmental conditions result in fewer and fewer non-GMOs each generation, and more and more GMOs gobbling up the resources on which both varieties depend. In agriculture, that is not even limited to GMOs that are not designed to be sterile, because more and more farmers will turn to the more robust GMOs rather than traditional non-GMOs.

Finally, herbicides kill plants (a case of doing exactly what is on the tin,) so GMOs that produce herbicides are as much a threat to other crops as they are to weeds.