Well ....... There is protein and then there is protein. All protein is not created equal. Proteins are built up from amino acids, and different proteins have different kinds of amino acids in them. Certain amino acids can be used to create certain other amino acids, so the human body only needs sufficient amounts of about
9 essential amino acids. Different foods have different kinds of proteins. The kinds of proteins found in rice, grains, fruit and vegetables don't have a lot of one of the essential amino acids - lysine, so to get this in reasonable amounts you need to consume legumes (beans, lentils, chickpeas, peas, peanuts) and/or e.g. seitan, which is made from wheat gluten, which is a protein that does have a lot of lysine.
So I don't agree with the claim that we get enough protein just as long as we get enough calories, or "just eat a varied diet" (since there is no universally agreed-upon definition of "varied diet".)
We have discussed this previously:
http://forum.veggieviews.com/threads/the-importance-of-legumes.3600/
Protein was also one of the issues underlying the problem here:
http://forum.veggieviews.com/threads/exploring-the-ex-vegan-phenomenon.3606/
(Apologies if I seem a bit arrogant in that first thread - a bit silly since I have occasionally wavered on the issue!)