There are ample ways in which one can benefit from veganism. People who often rely on food often have more health issues than one who is a veganism. Veganists often tend to be healthier and look healthier. Eating only vegetables, grains, legumes, fruits and nuts will help people lead much healthier lives, but it will require lots of self dedication and motivation.
Eating a vegan diet can benefit everyone. People who consume large quantities of meat often have to contend with diseases such as diabetes or high blood pressure. Eating a vegan diet can provide you with proteins that most people get from meat, without high "bad" fat content or lots of cholesterol and calories. A plant based diet can help to return previously sick people back to health.
It takes seven times as much carbon to make one pound of meat versus the same amount of vegetables. Everyone can benefit from veganism with better health, more vitamins and minerals and a smaller carbon footprint. The environment will improve with less animal waste. Soils will improve and there will be less strain on water resources. Feed won't be a problem as more agricultural crops will go towards humans instead of animals and there will be abundant food for everyone if everyone adopts a vegan lifestyle.
Veganism is entirely valid, but a lot of the food tastes disgusting. For me, there's room for vegetables in every diet... Right next to the mashed potatoes. With butter. Made from milk. From real cows. Also, what of fish? Fish are delicious, there's a ton of them running around, they Zerg-rush places on their own, and they are all-natural. While there may be clear-cut benefits from it for some people, I, for one, would not be an addressee, invalidating the "everyone benefits" part.
Some people at certain stages and ages of their lives may benefit from a vegan diet, but over the long term, there are going to be people who just are not going to be getting nutrients such as B 12 that are necessary for their health if they eat only vegan.
I think its just in our nature to eat meat. You can't get the correct diet in you system if you don't eat the right stuff. The protein intake alone is only going to be from soy and that's just not enough. Its certainly not the right diet for a man.