I was vegetarian for 9 months at one point. During that time, I was training for a century (100 mile bike ride). The hardest thing, because I was training, was how much I had to eat. Meat is calorie dense. The other hard thing is that I do most of the cooking for a family of four, and they weren't joining me in my switch, so I was cooking meat for them but not eating any of it. That can get old. But I managed the ride, and the lesson I took away was that it's not that hard. We have reduced dramatically the amount of meat we eat, and I shoot for vegetarian or near vegetarian meals as often as possible.
Partially that's because industrial agriculture contains pigs and chickens, but allows beef to roam (at least during the initial growth period). I do think they need less, even when raised humanely, but perhaps that chart is a bit skewed by the current model of raising animals.
People are mentioning organic a lot here, but remember that certified organic agriculture allows for plenty of dangerous pesticides. Copper based stuff as a fungicide, for instance. I haven't seen any good science that backs up the idea that organic on it's own is truly better. That doesn't mean it doesn't exist, but I haven't seen it. Organic coupled with soil health measures and land-centric agricultural practices, sure. But organic yields less per acre.