I may get slammed here, but feel the need to explain something:
When most scholars and activists discuss the connection between the Holocaust (or slavery) and the abuse and slaughter of animals, they are NOT trying to say that killing animals and killing jews, blacks, or ANY people are the SAME. They are instead trying to argue that the conscious enaction of cruelty and the knowing infliction of pain for reasons of personal gain (to make money, eat nicer food, have someone do work for you, or advance a racist ideology) is ALWAYS wrong. Cruelty is a moral outrage, no matter who the victim is.
It may, of course, be much more hideous to attempt to exterminate an entire group of people than it is to participate in torturing animals -- but both are unkind, cruel, and senseless. Just as it is "worse" to steal a million dollars from a children's charity than it is to take a twenty dollar bill from a wealthy neighbor -- yet both are still "wrong" and quite mean.
Unfortunately, the way that our modern farming and fur industries are constructed, animals are not simply killed as part of the "food chain." They are systematically tortured in the process. Many companion and work animals are also treated brutally throughout the world.
Though I don't always agree with PETA's practices, they really believe that they are living in the prescence of HORRIBLE cruelty, so feel justified in using forceful techniques -- just as so many people felt justified in standing up against slavery and genocide with violence.
Furthermore, many of you may be interested in ETERNAL TREBLINKA, by Charles Patterson. He demonstrates that the major architects of the Nazi Holocaust -- Himmler and Borman, for example -- had been heavily involved in animal agriculture and "genetic breeding" before they joined the nazi party. They applied their ideas about breeding "higher" types of animals to their vicious racial policies. Indeed, before the nazis tried to eliminate jews, they argued that the mentally ill should be sterilized and euthanized so that they didn't "breed."
Patterson further argues that the introduction of industrial farming and factory style slaughter-houses DESENSITIZED people to routine pain and violence. The people who watched cows screaming in agony while they hung from butcher hooks were "practicing" to torture people in similar ways -- they were learning to detach themselves from torture and death.
Anytime it becomes culturally acceptable to inflict pain and suffering on other living things it puts ALL people in danger. Everytime a child learns that it's not a "big deal" to set a dog on fire, or to torture a goose in order to destroy its liver and get foi gras, that child is being "prepared" to turn the other way when he sees human beings suffering.
Anyway, that's my long-winded theory about cruelty. It's always wrong no matter who the victim, and cruelty towards any living creature damages our entire culture and makes it more likely that we will be "prepped" to turn on each other. (of course the holocaust is much worse than the factory farm -- but they are absolutely related to each other in profound ways)
Btw, am I "perfect" about not using animal products in any way? No. Do I think about that fact and feel guilty about it every day? Yes. I don't believe that makes me a "better" person than anyone else, but I do believe that we should all try to be aware of the reality that we help to shape. Sadly, that reality currently includes brutal industrialized farming and fur industries, as well as many abused companion animals.
Another quick "btw" -- I do disagree with Peta's position on animals as pets and in zoos. I believe that well cared for and kindly treated pets and zoo animals can be just as happy as animals in the wild. Just as I am happier in an air conditioned house with indoor plumbing than I would be living in the "natural" condition, some animals may adapt nicely to modern life. It all depends on how they are treated.