Gene Healy discusses animal rights.
I just think this is a matter of degree. Look, if you're a vegetarian, you're still killing plants, which are pretty active creatures, just at a slower pace of action than we are used to. (Trees fight wars with insects, for instance, actively sending pesticides to places of infestation, and with other trees, at the root level.) And, in fact, you'll have to kill a lot of bugs or you'll get no crops! Placing some absolute divide between plants and animals is just "kingdomism."
The basic principle is, I think, the more conscious something is, the more we should treat it with respect, e.g., don't eat gorillas.
Rothbard argued against any animal rights along the following lines:
"One must also understand how the notion of rights developed. Why is it a common feature of man, and why do rights only exist in the faculty of human reason? This is because rights are grounded in the nature of man, who is a social, rational being. Only man possesses reason, and therefore only men can have rights. No other living being has the ability to reason, to make conscious choices, to use his mind, to pursue values, and to discover physical laws about the world."
This seems to me to be another case of Rothbard "figuring out" the empirical evidence based on the conclusion he wants it to support. How does he know no other living being makes conscious choices or can reason? I'd say that the ethological evidence today is overwhelmingly against him. And long ago, a Greek philosopher felt he had proved animals could reason as follows:
'Aenexidemus states that animals certainly possess the latter. The sensitivity, representation and intelligence of animals naturally depend on the body structure of each species. Dogs, according to Aenexidemus, possess the virtues of justice, courage and intelligence, and are even capable of using the fifth indemonstrable syllogism. In fact, upon arriving to a triple fork in the road, after smelling the two paths which the animal it was following did not take, it does not smell the third but immediately plunges in that direction without hesitation. This behaviour can be explained only based on the hypothesis that the dog makes the following syllogistic reasoning: "the animal has taken path A or path B or path C; but as it did not take A or B, it has taken C."'