Isn't this just the "yet you participate in society" meme? We all can and should attempt to reduce our impact, that might mean we don't own a car, or we fly less frequently and take trains instead, perhaps even just working from home... If I need to fly from North America to Europe, I really don't have a choice. You could do it by boat, but ships are largely powered by fossil fuels too. That doesn't mean I actively support fossil fuel companies.