Vegans make some good points when it comes to sustainability. It takes an ungodly amount of water to feed ONE horse or ONE pig, not to mention the countless amount of food and resources to raise and keep animals. There's also a huge problem with greenhouse gasses, which are a large contributor to global warming. Many of these animals are abused as well, which is a moral and ethical issue if nothing else.
Additionally, many meat sources are not as healthy as they may claim. Certain companies use parts of animals in their products which are not healthy or something that humans shouldn't be consuming. Eating a lot of meat is also not the best way to get protein: sourcing from various options like vegan protein powder is a good alternative to eating a lot of meat products.
Have you ever looked into deodorant? Major deodorant companies put aluminum into their products as well, which over time heightens and contributes to certain types of cancers. Check the ingredients list the next time you buy any beauty products. Anything with the term "fragrance" can be listed, and it isn't a real ingredient, it's a catch-all for other harmful substances.
Also, with the growing number of people in the world, it is becoming increasingly harder to feed all of them. It would be much easier to feed these people with plants than it would be with protein sources like beef or pork. There is also a lot of speculation on the extent to which meat is actually beneficial to your body in comparison with plant-sourced protein products. There are even vegan protein powders such as Orgain which prove that plant-based protein can pack a punch!
Finally, sustainability is a main argument in the case for veganism. We use way more resources than we produce, which is a completely separate problem in and of itself, but minimalism and simplicity are two huge ways that we are able to contribute to resource consumption. By sustainably sourcing things like makeup—there's some super bomb vegan makeup—we can all easily help the environment.