What should vegans feed their domestic cats to ensure they adhere to their ethical standards?

I’ve heard that the ideal cat food is a mixture of about 50% proteins, 40% fats and 10% carbohydrates. Is it healthy for the cat if all the protein comes from plants like soybeans? If yes, will cats actually eat it or do they refuse? If they refuse, will vegans try to prevent their cats from catching mice? What are good ethical guidelines? Might lacto-ovo vegetarian cats be a good compromise? What is your view on the topic?

From Wikipedia: Vegetarian or vegan cat food has been available for many years, and is targeted primarily at vegan and vegetarian pet owners. While a small percentage of owners choose such a diet based on its perceived health benefits, the majority do so due to ethical concerns. Cats are obligate carnivores and require nutrients (including arginine, taurine, arachidonic acid, vitamin A, vitamin B12 and niacin) found in meat sources that cannot be obtained in sufficient amount in plant sources. According to the National Research Council, “unsupplemented vegetarian diets can result in harmful deficiencies of certain essential amino acids, fatty acids, and vitamins.” Vegetarian pet food companies attempt to correct these deficiencies by supplementing their products with synthetically produced nutrients.

Organizations that advocate vegan or vegetarian diets for people have split opinions regarding vegetarian or vegan cat food. The International Vegetarian Union, the Vegan Society and Peta are some of the organizations that support a vegan or vegetarian diet for cats. On the other hand, the Vegetarian Society suggests people “consider carefully” and that many cats will not adjust to a vegetarian diet.

http://en.wikipedia.org/wiki/Cat_food#Vegetarian_or_vegan_food