The nutritional value of any diet, be in meat-based, vegan, or vegetarian, depends on the food you do end up eating. With a little bit of planning, meat-free diets can be equally or more healthy than meat-based diets. With a little research, meat-free diets can provide all of the necessary nutrients for a healthy diet.
And in the same way that some meat-free diets can be unhealthy, meat-based diets can also be unhealthy. For example, many processed types of meat like chicken nuggets are meat-based but are also full of chemicals and carry no nutritional value.
To dismiss vegetarian diets because there are some unhealthy alternatives ignores the fact that there are plenty of healthy meat-free foods too.