I have gone organic whenever possible to avoid the low-level antibiotic exposure as well as the growth hormones and pesticides. I want to live more ethically and to take personal responsibility and action against the awful treatment of plants, animals, and our planet in general.
Air miles are the last thing I think about. I think this planet has far worse problems than Planes right now. Organic costs more, but I would rather forego other things. Instead of relying on cars, buses, and trains for example, I walk or cycle, and I do think that's a bigger individual contribution than avoiding organic food from other countries, which I do think encourages good practice around the world. One step at a time for me.