GMO Foods Question + Petition for FDA to Label GMO Foods

Quick question - I understand there is research about genetically modifying plants and animals, specifically, mixing animal genes with plant genes. This is even more serious than genetically modifying a plant with another plant. Does anyone know if these foods are already being sold on the market in the US or elsewhere?

Also- I thought this community might want to sign a petition for the FDA to label GMO foods. I just don't get the downside of the labeling, especially when you're playing mad scientist with nature. Genetically modifying in the same way that plants or animals would get modified through evolution is one thing...but it doesn't seem to be the aim of GM community, the aim is to get these plants and animals to become something they wouldn't have otherwise for human purposes (e.g. less need for pesticide, longer lasting without refrigeration, etc.). 

Here's the website for the petition:http://justlabelit.org/take-action/

I'd love to know if anyone did thorough research on this debate, and specifically if you have any insights about the current or future selling of plants with animal/fish genes..