We just covered how vital integrating animal agriculture with crops is in my agroecology class! A huge part of the problem with industrial agriculture is how simplified it’s become with total segregation of animal and crop husbandry. Utilizing the two together is best.
There is an environmental argument for including meat and/or other animal products in the diet - essentially, animals can convert biomass that people CAN’T eat, to extremely nutrient-dense biomass that we CAN eat. There are definitely problems with industrial agriculture, and when it comes to animals feeding them all kinds of corn and soy is certainly an issue, it’s kind of wasteful when we could be producing food for people. But if we’re talking about grazing animals on rangeland that maybe isn’t suitable for crop growth (ESPECIALLY if native large ungulates have been removed and you’re careful not to over-graze), that’s creating food off land where we couldn’t necessarily produce any before. And in some cases we can use food that would otherwise be wasted and turn it directly into more food by feeding pigs with food scraps or a food waste-based product like Eco Feed. It’s cheaper than conventional pig feed, keeps food out of landfills, it’s healthier and more species-appropriate for the pigs (which are omnivores) vs. feeding just grain, and produces extremely high quality meat. It’s also a much quicker turnover of waste food to new food than composting, which takes a lot more time in the decomposition process (thus also needing more storage space for a longer period of time) before it can be applied to fields to even begin to produce more food. Composting is good, like definitely still do it, but our society’s capacity for composting isn’t at a point yet where we can compost all of our food waste, so aside from working to improve composting capacity and reducing food waste in general, diverting some to use as animal feed for species like pigs that can eat pretty much anything is a really great way to quickly turn food we can’t eat back into food we can and it doesn’t require as much new infrastructure.
Personally at least, being in the environmental field and having a particular interest in sustainable agriculture and particularly the intersections of animal welfare and sustainable agriculture, my feelings are along the lines of like…. it’s not necessary or probably even desirable to eliminate all animal products from our diet (on a large scale) to eat sustainably. There are a lot of really good reasons to keep using animal products, especially if we want small-scale localized food systems - there’s a reason you don’t typically see much vegetarianism historically and certainly not veganism. In most places if you’re growing food yourself or you’re only relying on what’s seasonally available from a small distance around you, you probably can’t meet your nutritional needs without some animal product intake. What I’ve found is that most people seem polarized into one of two camps: either “Hardcore Meat” or “No Animal Products Ever” and if you’re at all critical of our current problems with the animal product industries, you’re assumed to be against all meat eating/animal product use, meanwhile the side that pushes for no one to ever use any animal products ever again comes across as a little militant and unrealistic. What we need going forward from a sustainability perspective is probably something in the middle, more like how we used to eat - a reduction in meat consumption (assuming you eat the often extremely meat-heavy western style diet) and an increase in plant consumption, but still a good mix of both. Probably with a focus on less environmentally intensive animal protein options such as eggs, chicken, and milk with a move away from eating large amounts of beef, and ideally re-incorporating insect protein into a typical diet as it’s pretty much the healthiest and most environmentally sound complete bioavailable protein you can get.
I think a big part of it is just coming to terms with the circle of life. Animals eat other animals. We are not above that, and you are not alone - SO many people simply must eat meat or other animal products to be healthy and do not do well on a vegetarian or vegan diet, particularly in the long term. I know a few myself. It’s really not unusual at all. You don’t have to feel evil for eating the way that your body needs. This is how we evolved, this is how nature works. It isn’t evil, it isn’t personal, it’s simply life. It may come across as harsh to humans because we have Rules that we made with our big brains and we don’t really like thinking about violence or death mostly, but we don’t consider any other animal that eats meat evil for doing so. There is no malice behind it, it simply is. Are there problems with how humans specifically produce some of our animal products? Yes, but you can fight for better welfare of livestock animals without believing that it’s intrinsically wrong to eat animals. If you can afford to put your money towards small local farms that treat their animals well, do it. If not, you’re still not a monster - I’m a student, I don’t have a huge grocery budget, food is getting more and more expensive, and I don’t eat a lot of meat but what I do eat I usually have to buy as the generic supermarket stuff even though I don’t like how it’s produced. That too is part of life. It’s your body, and it’s your health, and you need to eat meat sometimes, and that’s okay, it’s natural, it’s not malicious or evil or some abberation of the natural flow of energy through the trophic web, it just is. Don’t let anyone make you feel bad about it. Do the best you can, but ultimately your health comes first. And I’m agreeing with the others here - don’t bother with people who try to vilify you for doing what’s best for your body. Keep them out of your life as much as you can. And it might be helpful to find other people who also couldn’t manage a vegetarian or vegan diet because I promise you are far from alone and many, many other people have struggled with this dilemma and the feelings you’re describing.