I am not 100% knowledgable on GMOs and I probably will never be...but I definitely support putting it on labels.
I think we should have the option to eat it or not and we should have labels to help us make those decisions. I don't personally care if they're on the market. Cigarettes are on the market, alcohol is on the market...but they have to be labeled as such.
I want to know exactly what's in my food. Sorry if some fat cat business owner loses out on some money to give me the freedom to choose.