I'm not a huge fan of stuff like GM maize. First of all, I'm not a fan of grains in general, and secondly, I'm wary of the additional pesticide. There are plenty of nuances, since the added pesticide seems a lot safer than what the corn would have been sprayed with otherwise. Also, I'm not well-conversed with the facts because I can't be bothered researching something that I try not to eat anyway.
What I don't have a problem with is the idea of manipulating DNA, or that it should only be done in a 'natural' way through selective breeding.
an example of healthy and natural genetic manipulation
Salmon 2.0 are simply designed to mature faster. Belgian Blue cattle are selected to be massively muscled. In the wild, these strains would quickly be weeded out because they are less efficient than their slimmer or slower-growing competitors. In the case of the Belgian Blue, the gene for myostatin, a muscle inhibitor, is messed up from a 'natural' mutation. In the case of growth-enhanced salmon, a gene string was transferred (transgene) from another fish. Why is one case evil and the other hunky-dory?
A big objection is that these modified salmon will escape and breed with wild salmon and screw up the species forever. I wonder why the same objections aren't made for dogs, cats, pigs, cows, and all the plant cultivars like grapes, wheat, etc? Is anyone worried that Cabernet Sauvignon grapes will suddenly escape and take over the countryside? Oh the tragedy! Or that Belgian Blues will breed with water buffaloes creating an African supercow that will take over the world and make us all wear bells around our necks? Of course not. A salmon that grows too fast, or a cow that has (literally) a ton of extra muscle it doesn't need would quite quickly be deselected in the wild. You can't screw up these wild species because they are already way better adapted to their environment than their modified cousins, whether modified by breeding or by adding a gene from another animal. These species we've modified over the past millennia (or in the last decade) are all hothouse flowers as far as Nature is concerned.
The real problem with these fast-growing salmon is that they will still be fed the same crap other farmed animals eat, thereby screwing up their n-3/n-6 ratio. Not to mention all the other unhealthy aspects of farmed animals: antibiotics, inadequate exercise, inhumane living conditions, etc.