Eating nothing but meats would be similar but opposite of being a strict vegetarian
Humans are not grazing creatures and must have animal protein and fats to a degree for health reasons.
Negatives:
Beside the above mentioned our abdomen would have to expand to accept larger quantity of low calorie food.

Beside economical benefits, there would be only negatives, (energy use and pollution).

Only by developing a contraption to turn solar energy into meat cells similar to plants photosynthesis, we could say that it is environmentally sustainable. Everything else is a transformation from one state to another or destroying one to create another.

Vegetarianism expands one field in economy while decreases animal husbandry to a same degree.

Only source I could mention is a common sense.

You could become anemic…without iron in your blood. and you may feel weaker and loose muscle mass….unless you take excessive vitamins