Just to state up front, I am a vegetarian who eats dairy food and eggs but not fish
For me the fact that plants don't have a central nervous system is a big factor in why I eat them and not animals.
I would also argue that that even though I don't eat any animal there are definitely degrees of moral importance when considering which animals to
If I had to eat a rabbit to survive (say I had crashed on a desert island), then I would and I would have no moral problem with doing so. I view
myself as being more 'important' than a rabbit. My death would be a bigger calamity than that of the rabbit not only because of my greater capacity
to reason, and feel emotions but also because of the effect my death would have on those who care about me. I would also have to factor in any future
actions on my part that lead to good and happiness for other people, which are likely to be more profound than those of the rabbit.
Now as I said before there are degrees of moral importance when considering this issue.
If I were to kill another human in order to survive that would be far more morally questionable. Likewise killing a chimpanzee would raise greater
moral doubts, although maybe not enough that I would sacrifice myself for the chimp.
However, at the other end of the moral spectrum, I could easily eat a fish in order to survive and not lose too much sleep over it.
And of course if there were plants available I would eat those. I don't think it's a defensible argument to say that a carrot has the moral
equivalence of a chimpanzee.
The reason I don't eat animals at the moment is because I don't have to, in order to survive, and this lack of necessity is what for me makes eating
animals morally wrong.
Another big factor in my vegetarianism is factory farming. I believe that chickens suffer far more in factory conditions than would lettuce grown in
the same conditions. I think this could be easily proved as well
Finally, I would add that it's extremely difficult to live a blameless life and the most that anyone can hope to do is to try their best. If the aim
of vegetarianism is to reduce suffering then that should be the motivating factor in all actions but the fact that sometimes you don't succeed is not
cause for giving up completely. If I accidentally bite into a chicken sandwich, that doesn't mean that I would then be morally justified in killing
a cow. Likewise, the fact that broccoli might 'sense' an insect attack doesn't negate the wrongness of needlessly killing a pig for food.