As someone who doesn't care at all about eating genetically modified foods, I expect the argument over labeling will break out soon. To fire the first shot: I really wish they'd label genetically modified foods. It seems a small courtesy for those who do have concerns. And those who don't? Well, we don't care. That's the point.
You are rational. Many people are not. Labelling a food as "genetically modified" is the same to them as labelling it as "radioactive" or "contains excrement".
I'm not sure if labelling food as genetically modified is a useful warning, or if it would be the same as saying "wifi used in this building". WIFI isn't harmful, and eventually it's going to be everywhere and not avoidable. Yet you still have people who claim that electronic smog causes all sorts of things.
I'm happy to eat these things. I'm gently worried about releasing organisms into the wild with "exogenes" (or whatever they're called). Evolution is amazing and powerful and wonderful. And human intervention in eco-systems isn't filled with particularly great examples - a long list of invasive species comes to mind.
How many buildings in California do you regularly come across with the "This building contains chemicals known in the State of California to cause cancer" or something to that effect? They are everywhere. It doesn't stop 99% of people from entering these buildings to work or live in them.
I actually do get the worry of changing the ecosystem. That's the biggest concern to me as well.
And I think I get your concern about the labeling as well. You're worried that people will assume the worst. I mean, you called it a "warning". But I expect it to be more like an organic labeling. Some people will care, most won't. Is it useful? Only to those who care.
If people want labels, they should demand them in the market. Don't buy foods that don't label. Do buy foods that do label. If they want to buy a food that doesn't label, write the producer and tell them you won't buy without a label.
I'm already seeing a number of products proudly claiming they don't use GMOs.
That's a lovely capitalist way to think about it, but it won't do much. Foods labeled non-GMO or non-hormonally-enhanced or whatever are only labeled so to target their market: the sorts of people who already care.
I'm making an analogy to the earlier remark that labeling things "has GMO" is like labeling them "has excrement" and "is radioactive."
"Has excrement" would certainly be perceived as negative, but the effect on my shopping of "has no excrement" would be a lot more negative (trying to find this sticker on everything I purchase, for example).