I usually assume anybody who worries about vegetarians and protein either has a very skewed idea of what regular not-really-terrible diets look like, or they just have no idea what they are talking about, or both.
As a vegetarian of possibly 10 years by now, I know my shit. I know what's going on in my body. I've had countless blood tests, and until recently, I've been found to be satisfactory (or absolutely phenomenal) in all areas. However, a couple of months ago, I was found to be seriously lacking in B12, which I owe to my recent reduction of dairy, making me nearly vegan aside from eggs, cheese, and other goodies, and slightly lacking in iron.
I now take 1000 micrograms of B12 a day, and two capsules of iron stuffs that I still can't understand the makeup of, I just know that it's a sufficient amount to keep me healthy. Never once has a doctor commented on my protein level. Never once have I been found to be anywhere nearing a "low" protein level. In fact I tracked my own diet for a week, and found that I overconsumed protein by a large enough margin to keep me safe from any sort of deficiency in that, save for a radical change in my diet.
And I'm a pretty typical vegetarian. I don't really slack off on my diet, but I don't pick over every little thing either. I should probably watch what I eat a bit more, and if I did, I probably wouldn't be underweight and deficient in B12 and iron, but one thing I've never had to worry about in the least is protein. I don't neglect my diet, but I don't really watch it either. This is probably easier for me due to my liking vegetables and fruits a whole lot. But I do get chocolate cravings, and I do binge, and the whole lot.
As has been said earlier, it would be extremely difficult for a vegetarian to be low on protein. You'd have to eat junk. And honestly, there isn't that much junk for a vegetarian to eat, much less a vegan. About half of all candy and sweets seem to have gelatin in them, making them unsuitable for vegetarians, and the rest have dairy products, leaving maybe 2% of snack foods for vegans, and probably about half suitable for veggie heads like me.
Vegetarians pretty much -have- to eat healthily. I can't imagine a satisfying vegetarian diet that is unhealthy. You could eat chocolate bars and potato chips all day, but even your regular joe schmo omnivore is nowhere close to that. Just as omnivores would like a filling meal, so would we vegetarians.
And to get that, you're going to get protein.
Honestly, almost all the food we consume has protein. Sometimes it is trace amounts, but it is enough. I would go so far as to say that protein is a non-issue for vegetarians. Pardon my ignorance, but what do you even CALL a protein deficiency due to diet? Have you ever heard of anyone with one, which wasn't caused by digestive or physiological problems? I sure haven't.
In western culture, a protein deficient diet is non-existent. Even in vegetarians, we are more likely to overconsume than to underconsume protein. I don't eat a lot either. I also go on stupid binges, like eating an entire cheesecake in a day. Yeah. I do dumb, ordinary things like that. And I'm healthy, now that I have my supplements, none of which include protein. I bike 20-40 minutes a day, on average. By my BMI, I am considered underweight for a woman in her early 20s, but I am not weak. I'm fit. And I'm happy. And I don't really watch my diet or care about protein. Hell, I don't even know how much protein I consume anymore, and I don't care, because I know that I don't need to worry about it.
When somebody asks me "How do you get your protein?" I instantly hang my head, and mentally run through the steps I'd have to take to get this person to understand that any diet, even vegetarian, would have to be terrible to be low on protein. I decide it's not worth it, so I tell them "eggs", which is at least partly the truth. This seems to satisfy them.
It's not my job to justify my diet to you. Please remember that when you dine with me. I don't ask you to justify your carnivorous tendencies to me. And if I am still here, not keeling over, and still riding my bike every day, you can assume I'm not dying for my diet.
Now to explain calcium...