Eating a balanced diet isn't hard as long as you don't eat the same thing basically every day (i.e. fast food). I think it's probably a non-issue, except for (say) naive teenage vegetarians - it's only a problem if you cut out meat but don't replace it with anything. I've done my research - if you have specific examples to the contrary, I'm all ears.

I ate a vegetarian diet for seven or eight years, a vegan diet for a few months* along the way, and have had a primarily* * vegetarian diet for years since then. I give blood regularly (I'm AB+, a rare donor blood type), and I've never, ever, ever had a problem with low iron - it's usually been quite high. While that's only one data point, it seems consistent with what I've read about nutrition - problems mostly occur when people give up meat but still eat a rather monotonous diet. ("In other news: Eating nothing but twinkies and whiskey is bad for you...Film at eleven.")

* I'm a cooking geek, and was interesting where those constraints would lead me.

* * same, plus fish and occasional Italian and French/Vietnamese charcuterie (Bánh mì!), but I cook/eat vegetarian by default.