OP, have you read Simon Fairlie's book "Meat: A benign extravagance", and also his articles on the topic of "Can Britain Feed Itself"
Would you say it is better to eat the products of a stockless farm which is largely dependent on imported fertility, or a mixed farm where there are few external inputs?
And indeed, am I being environmentally unsustainable if I trap or shoot the rabbits that are trying to eat my crops, and make them into pie. I'd argue that in this latter case at least it is hard to identify a more environmentally neutral source of protein in Britain.
Its a far more complex topic than 'meat bad, veggie good'. And that is speaking as someone who has spent more time than most people would consider reasonable reading about / experimenting with vegan-organic growing (because we don't have a reliable source of muck, and we don't want to keep stock for various reasons).
I lived for many years in an environmentally focussed land based community. It was notable that (I think 100%) all the people there who came from a town background were veggie, and none of those who came from a rural / farming background. Most of the latter ate little meat, and were very aware of where it came from, but they weren't veggie.
I'm not a green party candidate, though, and never likely to be 