I know a lot of people are very enthusiastic about soy, but I try to be cautious with it myself. I use soy sauce and enjoy edamame, but I make it a small part of my diet.
Just like any other way of living, you can be vegetarian in a healthy or an unhealthy way. Some people think being vegetarian means eating a ton of pasta and bread and nothing else. Those are the people who develop scurvy and other diseases
You need to be wise about your eating choices, just like every person does. Get a wide mix of foods into you so you get all the proper nutrients. Get the proteins your body needs. Take your multivitamins.
Saying "I will not eat animal flesh" is quite fine - many people live this way their entire lives! But saying "I will eat only pasta" is a death sentence
So it's a matter of looking at the nutrients your body needs each day and ensuring you get those into you. You can easily do that without eating piles of pasta or white bread.