GMO are a very powerful technology.
Like anything powerful, an intelligent person calls for caution.
A lot of people are worrying about GMO in food because we don't have enough data about them. We are changing things that could have important biological, health and ecological impacts, but the companies producing them are not willing to test them extensively for safety during 20 years before selling them.
We don't know what are the long term effects of cross breeding the GMO species with non GMO ones. We don't know the long term effects of the fauna. We don't known the long term (on decades) effects of ingesting any of them.
What we know is that if you give mouses the GMO food in isolation for a short time, they don't develop apparent problems. That's not a lot to go on, especially since very simple products, like processed meat, revealed themself as being carcinogenous on the long run (http://www.who.int/features/qa/cancer-red-meat/en/).
That's not science to me. That's business as usual.
I don't trust business. History taught me that for profit entities don't make the right decisions on this. After all, we knew asbestos was dangerous in 1920, but had to wait 1980 to act on it. After all, we fed cows with meat while knowing it's an herbivore, leading to spongiform encephalopathy. After all, we used the least safe nuclear technology we knew about because it was more suited for our military ambitions.
On a technology as complex as GMO, with a lot of interactions in different systems, it can take a lot of time to realize something is wrong. If it happens, it will take even more time before we act. The companies creating GMO will then, as usual, protect them-self to the extreme, and eventually just pay some money to get out of trouble, money they already earned by selling the GMO anyway.
So yes, whether it's GMO in food, nano-particles or anything that is very potent, I think it's fair to say "hey, slow down, we are not doing our homework here" when the other side is just trying to sell it to everybody.
It's a matter of agenda.