Why go plant-based?

There are three main reasons why we should eat less  – or preferably no – meat. Firstly, so that we may eliminate factory farms. Secondly, to reduce the shocking damage the meat production industry inflicts on the environment and its contribution to climate change (The Guardian). And finally, to improve human health.
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WHY I WENT PLANT-BASED (AND WHY WE SHOULD ALL EAT LESS MEAT)
BY JANE GOODALL 

Is there any evidence for the health benefits of a plant-based diet?

Plant-based foods are the most nutritious foods there are.  Even so, you will want to ensure that you get complete nutrition.  To do that, include a variety of vegetables, fruits, whole grains, and legumes in your routine, and I would suggest a special focus on green leafy vegetables.  And be sure to have a reliable source of vitamin B12 daily, such as a simple B12 supplement.  Vitamin B12 is essential for healthy nerves and healthy blood.   
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The Vegan Starter Kit: Everything You Need to Know About Plant-Based Eating By Neal D Barnard

Who are some famous athletes who eat plant-based diets?

1. Novak Djokovic: Number one tennis champion in the world...
Read More: 20 Who Athletes Swear by a Plant-Based Diet to Boost Performance 

do Vegan alternatives to meat made from plant protein extracts tend to be ultra-processed and bad for our health?
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The finding that vegans, vegetarians, and pesco-vegetarians consumed more of both healthy and unhealthy plant-based products and ultra-processed food products than meat-eaters is noteworthy. This highlights the heterogeneity in vegetarian diets and that those consuming a higher intake of the processed form of plant-based foods may not reap the health benefits often attributed to plant-based diets.
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Do plant-based ultra-processed foods improve the nutritional quality of vegetarian diets?

aren't Humans built to be omnivores? isn't  That why we have canine teeth?

Certain physical aspects of humanity have suggested that we are not cut out to eat meat on a regular basis. For starters we lack canines sharp enough to tear meat as a carnivore should. However, we do possess molar teeth which, like many herbivores, are accustomed to grinding down plant-based food such as vegetables and grains. Furthermore, the long digestive tract humans have are most like that of herbivores. Carnivores utilize short digestive tracts to extract the dense nutrients within meat easily. Long digestive tracts, however, are specifically adapted in herbivores to extract cellulose from green plants, which brings us to the question, if humans were not originally adapted for a plant-based diet, why were their bodies built in such a way. 
Were humans made to be herbivores?

isn't it the safest approach to eat moderate amounts of a very diverse set of whole foods, including meat? Is it risky to exclude animal products from our diet altogether?

Plant-based diets carry some risk of inadequate protein, vitamin, and mineral intake. But these risks are readily overcome by choosing the right vegetarian foods and, when necessary, supplements. For example, soy, quinoa, and nuts are good sources of protein, and tofu, lentils, and spinach are good sources of iron.
Plant-based diets are best… or are they?

what are good sources for plant-based vitamin b12? 

Natural foods such as nutritional yeast, yeast spreads, certain mushrooms, and some algae also contain vitamin B12.
Top vitamin B12 foods for vegetarians