The industrial animal farming industry has many problems.
Animals are not treated ethically in the slightest. Beef cows are confined shoulder-to-shoulder and can't move. Chickens are packed tightly together, and end up attacking each other. Hundreds of millions of male chicks are killed a year because they aren't suitable for meat production. After birth, calves are separated from dairy cows.
To prevent these animals from getting sick antibiotics are put into their feed,
80% of US antibiotic use is from livestock. This makes it a contributing factor towards antibiotics resistance. For example, resistance to Colistin, a last-resort antibiotic, was
found recently. What was the cause? Farmers had been giving Colistin to animals for years, and resistance eventually made it to human pathogens.
The industry has a very large environmental impact.
15% of greenhouse gas emissions are created by the meat industry.
26% of Earth's landmass is used for livestock.
27% of freshwater consumption is from livestock.
So, the answer is to stop eating animal products, right? Imo, no. In the short term it may help, but I'd argue that it doesn't help in the long-term and that there are better alternatives.
Why? I'll first address the environmental aspect, specifically land.
11% of land is used for crop production including (I assume) the crops being used for livestock. Can we more efficiently use land for growing crops? Of course. GMO crops, whether you like them or not, can and have increased yield. Vertical farming methods such as hydroponics and aeroponics can reduce area significantly, some speculate by up to 20 times (although I couldn't find a source for that). This would help with our habitat loss problem.
The treatment of animals, I suspect, will get better in the coming years. The reason I suspect this is the invention of cultured meat, meat grown in a lab setting. Various startups are working on mass production right now, so it likely won't be long before we have at least affordable lab-grown meat. This wouldn't cause factory farming to cease, because most likely it'll still be cheaper and some may find lab meat unethical. However, if people buy it enough over conventional meat, it could mean less animals are farmed, potentially giving them better treatment.
For greenhouse gasses we can use genetic engineering. Various methods are being testing for this, but this post is long enough. XD
Or we could all stop eating meat, right?
One problem with not eating meat is that our ancestors evolved to eat meat. As a consequence, there are some nutrients we need that are either hard to get from plants or not found at all in them. Vitamin B12 is
absent in plants for example. Many nutrients are more bio-available in meat than in plants, meaning it takes more time and energy for your body to get less from plants. Examples are
Iron, Zinc, and
Selenium. On top of this, plants containing protein often
lack a few amino acids, whereas meat has all of them. You have to be very careful, or you may end up with a deficiency in something.
If all humans stopped eating animal products, as others pointed out, most livestock would die anyway. What do think would happen to the roughly 30 billion animals being kept as livestock? If eating their products was outlawed, there's no point for big companies to feed them anymore. They'd all be slaughtered and their meat wasted. You might be able to save some by adopting them, but you cannot possibly save all of them. That's not to say I think they'd go extinct, enough people like them as pets (chickens for example, are very adorable).