>>> But in this instance only a single gene is used.
One has to start somewhere!
>>> There are however "backups"
Even if that were true, (which I doubt), what you would have to do is make sure all traces of the errant gene were destroyed from the environment before you could introduce the clean stock, otherwise the same things would happen again. How do you/they/them/whatever propose to do this? What plants/animals are carrying but not expressing the gene? Scorched Earth policy?
>>> been crossing plants since recorded history.
>>> we're only seeing something that we've done 10000 times before,
Not true. When crossing plants, the species involved have to be moderately closely related for the crossing to produce a viable result. Yes, you can pollinate a lupin with another lupin, but how would you begin to "cross" a tomato with a flounder? (Answers to alt.sex.tomatoes!)
>>> I just want the choice to buy/eat these GM foods or not.
Me too, however, in a recent BBC survey, 40% of samples tested for GM soya in "Non GM" labelled foodstuffs contained markers for GM. It is thought that some of it arrived simply by unscrupulous people falsely labelling their raw materials, however, this did not account for all cases, and it is suspected that the markers arose as a result of cross pollination of non GM crops from GM sites.