Exactly - it's choice, and it's a personal decision.
You deride the value of meat, yet gram for gram aren't both lean red, white, and fish meat proteins more useful, easily digested, and nutritious, than the equivalent from vegetable sources? Especially if we're talking about organic and local product as opposed to factory farmed animals?
Also, nuts proportionally contain a lot of protein - but also a lot of fats. Someone who got all their protein from nuts alone might find themselves facing other health issues?
As ever, variety and moderation are simple truths when it comes to diet.
The bizarre thing is that this discussion is being continued by vegetarians, who for the most part, regard diet as personal choice.
I just personally find evangelising diet choices to be somewhat sanctimonious, especially as there are so many different facets of any individual's modern life that can easily subjected to criticisms from so many ethical angles - that I think someone who stands on their soapbox about vegeatarian (or vegan) issues really needs to demonstrate white-than-white credentials.