As stated before "GMO" is a big term - it is the outcome of a technology, not a religion or ethical principle. As such it is neither good nor bad - however it has effects, and we as a society get to decide whether the effects are desirable or undesirable. We make these conclusions based upon our bias, which is present in every human (it is what defines us as individual humans I would submit).
Every study and organization cited in this thread is biased. That is life as a human. That being the case, I argue we should make population-based health decisions from the perspective of the precaution principle.
Money talks, and money funds research. It is very difficult to get good studies funded for natural non-patent-able substances, or procedures which are not protected by a particular guild. The status quo will protect itself with all it's might. - consider the case of Dr. Tyrone Hayes - who was blackballed http://www.newyorker.com/magazine/2014/02/10/a-valuable-reputation for publishing his work on Atrizine causing mutations in frogs in the Proceedings of the National Academy of Sciences http://www.pnas.org/content/107/10/4612.short
Do you think research that comes out contrary to Monsanto is going to be treated any differently? Unfortunately, the individuals that have already lost it all, or are so bull-headed they will not bow to the pressure are often characterized by having very low emotional intelligence. Geesh, some of the things 'advocates' say.
In the end, I have a hard time believing much of what is published, because with any talent whatsoever a researcher can report outcomes that are favorable to the bias presnet... and funding is a strong bias. So, safe? Not safe? If you will have science be the standard is WAY too early to make a determination either way given the lack of decade-long human studies using organic controls, and conventional non-GMO controls (each of which may come out differently). Expensive ? Nah, not compared to doing this wrong and forever altering our inner and outer biomes.