Junior year of college I met for the first time a vegetarian who had chosen that lifestyle not for ideas about animal rights, but instead because he was concerned about the loss of energy that meat production caused. In other words, cattle and pigs aren't 100% efficient in converting the grains they eat into meat for us to eat -- not even close. So, theoretically, if that grain went into feeding humans instead, a lot more people could have enough food. (I also read an article or two to the same effect.)
Fast forward to this year, when I started doing a lot of reading on various social issue/cause blogs. I came across one very frightening defense of abortion which included a line like, "In any case, the world is vastly overpopulated without enough food to support everyone, so. . . " So? So any way we can kill off a few more people is probably a good idea?
My brain short-circuited the two ideas together, and came up with: I should be vegetarian to support the pro-life movement. The less I consume, the more food there is available for non-aborted babies! Yay!
But, somehow (as always), my intentions did not match up to my actions, and although I stopped buying chicken earlier in the summer, I continued to purchase cans of tuna and sliced ham (for my green beans!) and so forth. . . (Side note. I'm going to guess the reason that tuna is so cheap compared to other meats is because no human effort has to go into raising them for munchies -- as opposed to us growing grain for cows, etc. However, tuna is not a non-problematic meat (ARRRRRRGH) because (so far as I know) overfishing is driving them not-so-gradually to extinction.)
However, I think my budget crunch may do what my social cause guilt may not: Switch my sources of protein to beans, milk, and eggs. Why? Well, let us compare chicken and beans.
Note in particular item #1 on each list.
And, in the unlikely case you are fussing about how much protein I eat, I just checked and I pretty much meet my daily requirement in wheat protein from pasta alone.