They are wrong in that calcium, iron, and zinc are only available through meat. You get those from green leafy vegetables, and nuts or seeds. The reason why meat is known to eat for iron specifically, is because it has saturated fat which enhances it's absorption, while plants have no saturated fat, but that is why nuts or seeds are important to have in your diet as they contain enough saturated fat as well as being high in anti-oxidants so the saturated fat doesn't create too much cholesterol which when oxidizes causes problems which happens when you eat meat, that has very little or no anti-oxidants. Even something simple like sauteing your greens in some ghee(clarified butter) or coconut oil will enhance iron absorption. So meat is not needed to get iron in the diet.
A lot of people who claim being a vegetarian didn't work for them usually ate processed food which are void in key nutrients, when they should have been eating whole, natural, "peasant" foods, but you need to know how to cook to enjoy these foods. If you want to be a vegetarian, you have to learn how to eat, which means learning food, and the body, being that the knowledge isn't really out here. Once you do, and workout properly, NO ONE can fukk with you on this health shyt, and getting fukked up if you puff herb, and drink as this diet sensitizes your body, while also strengthen it. Don't make me go into sex, these chicks will love your ass but that takes some more knowledge.