1) Eating farmed meat is bad for the environment because it is usually done in a way that is an unsustainable overuse of resources.
2) Being vegan can actually be worse for the environment than not, due to the way a vegan diet uses land and the way that vegan substitutes such as almond milk are created.
3) Eating lots of meat can be bad for your health, but eating no meat and/or no animal products (eggs, dairy) can be even worse, due to lack of vital nutrients found primarily in meat and animal products.
4) Being in control of your own diet is a privilege that many poor people do not have, and it is unethical and cruel to tell them to cut necessary nutrients out of their diet whem they have no alternative way to get them.
I went vegetarian in April 2009, when it was first pointed out to me that even if you only consider water use, meat is an extremely resource-wasteful food. I was worried that I wouldn't be able to function without it, so I kept it a secret for 6 months so that if I failed, only I would know about it. I was able to maintain my energy levels without eating meat, so I didn't eat meat from then on.
It wasn't until April 2014, five years later, that I accidentally realized that I had a massive nutritional deficiency. I was on tumblr and saw a necklace with a molecule that the artist referred to as "memory." Since my memory had been getting exponentially worse over the past few years, I looked up this molecule, acetylcholine. I learned that a major building block of memory is choline, also called b-11, which is obtained through eating meat, especially
I immediately ordered choline supplements, and when I started taking them I saw a jump in my mental capacity. When I ran out I noticed it even more as without it my mind was slow and stuttery and constantly forgetting. I have been on a high dose since then. I have since learned that all medications for dementia that are currently used in the US work on choline. This affirmed what I already knew, that choline is incredibly vital for cognition. Further, eating fat with choline is necessary for good absorption, so a low-fat diet can create the same problems as a no-meat diet.
Now you can get enough choline in your diet without meat or supplements but the primary sources are going to be animal products such as eggs (2-3 eggs a day will do it) and dairy (whole milk, cheese, yogurt). Otherwise the amount of veggies, legumes, and/or beans you would need to eat daily to get the right amount of protein and nutrients is so extreme the vast majority of people would not be able to do it. I love spinach more than most but I'm not going to eat a pound of it every day. If you are not a nutritionist and meal planner, not able to hire a nutritionist and meal planner, and not able to spend hours and hours essentially learning to be those things, you can't eat vegan and be healthy, in my opinion. The problem is that deficiencies show up very slowly, so you're not going to notice them until they're pretty bad.
The other main nutritional deficiency I developed was for amino acids. I didn't know these are primarily sourced in meat, because nobody seems to have ever accounted for vegetarians in any of the nutritional literature I could find. I discovered my deficiency because after one outbreak of herpes 5 years ago, I had another in February 2016, and then I had another in March, and another in April. This was really weird because usually they increase in time between re-occurrence. So I started taking lysine supplements daily, and I haven't had an outbreak since.
However it didn't occur to me to look into other amino acids until a few months ago, when I realized I needed to supplement for histidine, phenylalanine, valine, threonine, tryptophan, methionine, isoleucine & leucine as well (your body can't produce these). Fortunately some of these are easily available in full-fat dairy such as whole milk and cheddar cheese. For the ones that are not, and to be sure I am getting enough, I also ordered dried egg powder that I can mix into my morning protein shake. It has a good amount of all of them, it doesn't taste bad, and I found what seemed to me to be an ethical source.
If you are not prepared and able to buy and take supplements every day I would encourage you NOT to go vegetarian but simply to reduce the amount of meat you eat. Most US people eat more than they need: you only need an amount that is about the size of a deck of cards each day, and less than that if you eat other sources of protein -- and most people don't need meat every single day, so maybe skip one day a week. But when you do have it, please eat it with a fat so that you can properly absorb the choline.
(also, if there is ANYTHING that you eat a lot of on a daily basis, I urge you to look up its effects, especially if your hormones are sensitive. A lot of people suggest soy as a source of vegan protein, but it will disrupt your hormones so unless you need more estrogen I do not recommend it. I think eating soy every day for a year and a half contributed to one of the worst depressions I have ever experienced. Soy is getting to be well-known for increasing estrogen, but flaxseed, sesame seeds, and chickpeas have similar effects -- flaxseed to a much higher degree than soy.)
I will never go vegan because I find it difficult to eat as it is, and without eggs and dairy I would have to spend so much more time researching, shopping for, and preparing food. I would end up going hungry much of the time, I wouldn't be able to ever eat enough to get all my needed nutrients, and it would harm my health. And if I became poor again I would have to stop, and adjusting back to animal products would be hellish until I built up my microbial communities again.
If you do go vegan, please consider the environmental and human costs as well as the cost to animals. For example, I consider it far more ethical to drink local animal milk than to drink almond milk sourced from California almonds, since California is in drought and should not be producing such a water-greedy crop. When I looked it up, cashew and pea-protein milk are both more gentle on the environment, so you may want to look into those.
Another important consideration is that many farms which produce vegan imitations of dairy and meat products do not treat their human workers with dignity or offer safe working conditions, and these bad conditions disproportionately affect people of color, women, and children. So if you choose to be a vegan to reduce the suffering of living beings, you have an obligation to look into the sources of your food so that you're not simply shifting the suffering onto humans who do not have your privilege.