But, living things are not machines. Machines don't remake themselves. The difference between dealing with dead and living things is like the difference between kicking a football and kicking a dog. But when you kick a dog, you don't know what's going to happen. The dog may lie down and whimper, yelp and run, stand and growl, bite your foot, or wait until your back is turned and take a hunk out of your backside.
Genetic engineering is a lot more like kicking a dog than kicking a football.
Scientists just don't know what's going to happen. Thus, when genetic engineers insert a new gene into a living organism, the context of every other gene in the organism has been changed. They may have a pretty good idea of how the new gene will express itself, but they have no way of knowing how the expression of any other genes may be changed, particularly in some future generation of the organism. In order to assess risk, one must at least have a reasonable estimate of the distribution of possible future outcomes or occurrences. With biotechnology, we don't have a clue.