Ecoli:
First of all, as I had already said, the argument that GMOs will stop hunger is a false one since this is a political issue.
Second, nowadays scientists are thinking ahead like never before... germplasm banks are emerging and are a very nice way to preserve the variety of species. (and everybody knows that less variability can lead to extiction... there's no need for you to mention that again and again).
And to finish... when you introduce a new gene/trait into a plant you create MORE diversity in certain species. This diversity is lost in agriculture/selective breeding, and this happens with GMOs and not GMOs. As I've said, it's up to farmers to select the best varieties (with GMOs they have MORE varieties to choose from...).
Oh! And of course genes interact with each other... but you can't forget that GMO's are intensively tested before coming out to the market (if they are not banned... as it is in Europe...)