Dogs don't need meat - they've evolved to eat whatever humans eat - not sure why that's not true for cats as well because they've both been domesticated about the same amount of time, I think. But my mom's dog was cooked vegetarian for years and was radically healthier and noticeably HAPPIER.
dogs have been domesticated for 20 000 years and cats only 5 000. cats have many years to go before they can survive without meat
I have two wolf-hybrids, high percentage wolf, that I raised from pups. They got frozen carrots wen they were teething, and still love their veggies as treats. I still do give them chewies/rawhides because they need those things. They do need meat products since that's what they eat in the wild, so I'm not going to force them to go all vegan. They get diarrhea from too much veggies. The reason I think carnivores need veg in their diet though is because when they kill an animal they eat the stomach content=vegetation. That's why our dogs/cats will ingest grass. Cats require Taurine which is in most commercial cat kibble. It's also in nutritional yeast but reality is - by nature's design dogs/cats are carnivores. Period. You can feed a dog vegan as per Durianblossom's post however you really need to know nutritional requirements and be prepared to measure out correct amounts of protein/fats/carbs. I use a high quality commercial kibble and supplement with dog-safe veg and brown rice.
As for cats eating bananas, my cat would never touch fruit. Cats need Taurine found in animal products. It's also in nutritional yeast but again, most owners are too busy/lazy to ration out and study what's needed to make their own home made pet food. Know what happens if I put my wolves on a vegan diet? They start killing all the birds in my yard...gross. Supplementing veggies/fruits is fine for that reason but forcing a carnivore to eat only vegan? I say no. My 14 year old rescue mutt is still running around like a pup, my cat lived to be over 20 years old, they were fed meat/veggies which was a great balance. Just speaking from my personal experience. Regarding the real topic of this thread....my brain does WAY better on vegan :) My pets can have the meat.