There's research involving many crops on how gene flow works and the fact that mother nature will always surprise you. The way I look at it, there's nothing that is not possible in biology, but you can determine scientifically what the barriers need to be. If you think of it from a continental point of view, if it's going ahead in the U.S., it's going to be here anyway. It's going to move. You're going to see some flow.
Scientific studies can be done to at least create some kind of system whereby people would feel protected, but as you said originally, it's quite an emotional issue. I don't know how you deal with emotion, other than through education.