In conventional breeding, the biologist promotes good genes (genes that express physical traits that make the organism economically more valuable) through natural reproduction. The breeder though gets to choose who mates whom. The end product is a genetically modified organism.
In genetic engineering, the biologist shortcuts the reproductive process. She isolates the gene of interest, and inserts it (I'm an economist, don't ask me how) into the DNA of a subject organism. The end product is a genetically modified organism.
So should you eat your genetically modified corn? Your already are!
Now a mad scientist could set up an experiment where, by conventional breeding, he develops a really tough termite that resists the usual pesticides. Or he could try to do the same thing using genetic engneering. If he has access to facilities and personnel, the latter would probably be faster. But the end productive is the same - an unusually destructive termite that could inflict billions of dollars of untold damage.
Now suppose our biologist grows a conscience and instead chooses to develop a type of corn that resists pests. Similarly the latter would probably get her there faster, but with similar results.
But wait! Isn't genetic engineering dangerous? Might as well ask: is conventional plant breeding dangerous?
Actually, YES - the products of conventional breeding have inflicted great costs on the environment. Monocrop agriculture is the global norm, with the resulting erosion of genetic variability, intensification of chemical application, etc. Not good. But yields are up, way up. Not bad. We take the bad with the good. That's why even environmentalists don't paddle a canoe to attend their global confabs.
And genetic engineering? A faster way to get the benefits - and costs - of conventional genetic modification.
Don't believe me? This Reason page has plenty of links to get you started on the science of GMOs. Happy enlightening!