I can see the issue from plenty of perspectives - good and bad.
There is certainly potential in the science - to me there is no doubt that - but so long as greed (i.e. companies that get to "own the rights" to life, purely for profit) is a ruling factor the actual positive of the science, and the ability to be responsible with the technology, is greatly over-shadowed and hindered. Profit demands haste, and haste makes demands. And when it comes to the science of life itself - an area that needs careful patience and time, plenty of time (as I'm sure we all experience in our growing efforts lol) - haste and demand are essentially the opposite of a healthy environment and a bane on scientists.
Essentially, the biggest issue with them isn't -really- them, but rather greedy & reckless people.. which tends to be the core matter of so many issues.. In the case of GMO's, that happens to be corporations that have gotten away with having rather obscene amounts of power & control over both market & government.
That's my opinion. *nod*