If we suddenly stopped eating meat, we would put several species into extinction. Maybe that would be an acceptable loss, but letting several species go extinct to "prove" how wrong we humans are would not be the way I would promote ecological improvement.

Better to deal with the issues where they are. Over fishing should be dealt with. Countries are just now realizing that the sea doesnt stop at the border. If they could put so much money and effort into ACTA/SOPA, then maybe they could put some energy into fixing this? If US can put countries in a naughty list because some country didn't jump and enforce to US copyright law, maybe EU could put countries on a naughty list because they don't follow follow fishing rules.