As for 'sustainable' agriculture, the reality is much uglier than the poster would like you to think. The yields are much lower, think 10x lower, pre- green revolution levels. This means that the cost is significantly higher - but also that it much more land and capital intensive. Huge incentives for deforestation.
Heck, a truly sustainable agriculture would use only bio-fuels which is barely breaking even energetically, so for each acre of wheat you would need a few more acres of rapeseed or corn to produce the bio-fuel required.
All in all, you could say that meat consumption is killing the planet. Since people seem to like meat, the logical conclusion is that we should dissuade them to eat it via a higher prices. Those higher prices would be the natural result of producers internalizing the costs of environmental destruction caused during production, incentivizing the use of sustainable methods.
But if this is what you believe in, then take a political position and be prepared to fight for it: "We need more expensive meat, and we need it now !". Don't beat around the bush with the "greedy corporations" conspiracy that are killing the planet for "profits".
[1] http://www.geneticliteracyproject.org/2013/10/22/michael-pol...
The problem is overpopulation.
While overpopulation is a problem the way we think about food doesn't help. If you look at food production in countries with high ovepopulation (like China), you will see that the diet contains a lot less meat than our western diet.
Raising animals at the scale that producers here do has side effects ranging from land and water pollution. The pollution, animal waste and byproducts of their processing also high lights the over use of antibiotics in feed.
