Increasing pest and disease resistance is one of the most common reasons behind primitive genetic modification. Wheat, in particular, has gone through significant alteration (mostly through selective breeding) to increase it's resistance to certain diseases and pests, improve hardiness, etc.
My point is just that we're not doing anything different than we've ever done. Our technology is just advancing, and theoretically that means we can actually create safer alterations to genetics because we can employ more surgical and thoughtful techniques.
And actually, we've caused certain problems with even our primitive tinkering. Again, wheat in particular was recently (mid-20th century) modified significantly to help India solve famine. There have been a lot of unintended consequences as this strain became common place. One research firm is investigating using recombinant DNA technology to "undo" this strain and return wheat back to what it was in the early 20th century.
Science is cool, jb. It's what makes humans awesome.