So, dogs are what they call “opportunistic omnivores”. Wolves are carnivores, but as dogs became domesticated and scavenged around with humans, their bodies adapted to digesting plant material.
Now, “being able to digest something” and “requiring something” are two different things. Dogs need meat to thrive and be a happy, healthy animal. They can “survive” on a plant based diet, but I’m not sure why you’d choose to just “keep your dog alive” versus giving them the proper nutrition. Even your dog’s anatomy is designed to eat meat. Their teeth, the way they eat, and their digestive system are all designed for meat.
Here is a more in depth article from @why-animals-do-the-thing
http://www.whyanimalsdothething.com/posts/carnivores-and-vegan-pet-food
Now hold on. @why-animals-do-the-thing also made a great post about the difference between abuse, cruelty, & neglect.
If someone chooses to put their dog on a vegan diet strictly because of their morals & beliefs, they are being neglectful. They are unintentionally causing harm to their dog and simply need to be educated.
If someone understands that dogs need meat, but chooses not to do so because of their morals and beliefs, then they are being cruel. They are intentionally harming their dog because they are prioritizing their morals over their own animal’s welfare.
Abuse is intentionally causing harm to a dog with the desire to cause that harm. I don’t think anyone feeds their dog a vegan diet with intent to hurt their dog.
Calling someone any of these terms is the best way to prevent them from learning and changing. Accusing someone of being abusive is wrong, and often only creates denial and avoidance.