I may be the only vegan (self-proclaimed, at least) who has actually performed the infamous LD50 test. LD50 stands for the lethal dose that causes 50% of the population to die. I did it for a limnology lab some weeks ago, we were testing lead toxicity in zooplankton. Before we started I heard that some people in the morning class objected to doing this test because it would kill the zooplankton. I don't know if they were even vegetarian.
While I'm usually against animal testing, I didn't object, and carried on with the test. Some people might think that this makes me a hypocrite, that I'm assigning a hierarchy to the worth of an animal's life based on anthropocentric values, or something or the other. But I'm not. Actually, I don't think life has any intrinsic value at all.
I'm not vegan because I'm against death, but because I'm against suffering. Some pesky philosophy majors may disagree that suffering is to be avoided and pleasure is to be sought out, but to me it's just one of those things that's painfully obvious. Death, on the other hand, is only bad for the ones who stayed alive (at least for humans).
I firmly believe that different animals have different capacities for suffering. I would never compare the suffering of an circus elephant with the suffering of a zooplankton with lead intoxication. Most people intuitively think so as well, but it somehow gets lost in veganism's First Commandment, "all animals are equal".
We know that other mammals have brains much more similar to ours than to reptiles', which are much less complex. We only know what we ourselves feel, and we can't infer that all animals suffer the way we do because the only suffering we know is ours. So it's not a far cry to assume that the more similar an animal is to us, the more they will suffer the way we understand suffering is. Sure other animals can suffer in different ways than we do, but an animal whose brain is not nearly as complex as a mammal's can't possibly suffer more, and most likely not as much.
Everyone has to draw a line somewhere. A lot of vegans draw the line at microscopic organisms, but why? Can they not suffer just because we can't see them? Is it because they are small? Do smaller animals suffer less? Many will say that the line is drawn when they are detrimental to us, but a lot of them aren't harmless at all, like the mites that live on our follicles (picture on the right), yet we still kill them when we bathe. Mammals can also be detrimental, like the goats destroying the Galapagos islands ecosystems, but no vegan would ever suggest that it's okay to kill them. The "detrimental" argument is a bad excuse, then. Many vegans are also against killing sea sponges, which have no nerve cells at all and are pretty much indistinguishable form plants and fungi. So why is the line drawn there?
The truth is that there really isn't a perfect line to be drawn anywhere. The sheer concept of a line to be drawn implies a gradient of which animals are to be saved and which aren't. If there is a gradient, then, why look at things as black or white?
I've killed zooplankton. I've also killed plenty of bacteria, fungi, insects, and even some arachnids here and there. Is that really as bad as killing a deer, or a cow? Really?