Killing them for sustenance is nutritionally unnecessary for survival, therefore it's immoral to take an animal's life to feed yourself. Humans can happily live on a completely plant-based diet.

American Dietetic Association

It is the position of the American Dietetic Association that appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes.

Dietitians of Canada

A well planned vegan diet can meet all of these needs. It is safe and healthy for pregnant and breastfeeding women, babies, children, teens and seniors.

The British National Health Service

With good planning and an understanding of what makes up a healthy, balanced vegan diet, you can get all the nutrients your body needs.

The British Nutrition Foundation

A well-planned, balanced vegetarian or vegan diet can be nutritionally adequate ... Studies of UK vegetarian and vegan children have revealed that their growth and development are within the normal range.

The Dietitians Association of Australia

Vegan diets are a type of vegetarian diet, where only plant-based foods are eaten. They differ to other vegetarian diets in that no animal products are usually consumed or used. Despite these restrictions, with good planning it is still possible to obtain all the nutrients required for good health on a vegan diet.

The United States Department of Agriculture

Vegetarian diets (see context) can meet all the recommendations for nutrients. The key is to consume a variety of foods and the right amount of foods to meet your calorie needs. Follow the food group recommendations for your age, sex, and activity level to get the right amount of food and the variety of foods needed for nutrient adequacy. Nutrients that vegetarians may need to focus on include protein, iron, calcium, zinc, and vitamin B12.

The National Health and Medical Research Council

Alternatives to animal foods include nuts, seeds, legumes, beans and tofu. For all Australians, these foods increase dietary variety and can provide a valuable, affordable source of protein and other nutrients found in meats. These foods are also particularly important for those who follow vegetarian or vegan dietary patterns. Australians following a vegetarian diet can still meet nutrient requirements if energy needs are met and the appropriate number and variety of serves from the Five Food Groups are eaten throughout the day. For those eating a vegan diet, supplementation of B12 is recommended.

The Mayo Clinic

A well-planned vegetarian diet (see context) can meet the needs of people of all ages, including children, teenagers, and pregnant or breast-feeding women. The key is to be aware of your nutritional needs so that you plan a diet that meets them.

The Heart and Stroke Foundation of Canada

Vegetarian diets (see context) can provide all the nutrients you need at any age, as well as some additional health benefits.