If a PETA activist and I were trapped in the mountains, say at a place like Donner Pass, I know who'd survive.
The reason he is a vegetarian is that he is a retired Doctor of Veteranary Medicine and is well informed about the antibiotics and hormones that our meat (particularly beef) get so as to get big and fat fast and not get sick before they are sent to market. He thinks that if he eats these meats he is ingesting these drugs which would be less than beneficial to his long term health.
I don't know if I buy his rationale, but I certainly won't debate it with him. Furthermore he doesn't care whether I eat meat or not.
But if you get stuck on Donner Pass with him (he actually lives nearby), I wouldn't recommend trying to eat him.