Forbinator, you have my respect for being vegan. However, there's too much Peter Singer-style liberalism in your post.
We are surrounded by speciesism, but with no justification given for exactly what the relevant differences are between people and cows (for example) that make one ok to kill but not the other, because it is so ingrained within society. Everyone we know is ethically opposed to the murder of innocent humans for food/pleasure/entertainment etc. yet they fail to extend this same position to other sentient animals based on a naturalistic fallacy ie. "but the cavemen did it!" or "but lions eat zebras!" as if cavemen and wild animals are a reasonable model to base one's ethics upon in civilised society. Adopting caveman/lion ethics is effectively the same as dismissing ethics altogether, which could be a logically coherent position as long as you don't complain if a beloved human is murdered.
It's true that the position of society is moronic and incoherent - however I don't think it's a good idea to confuse modern carnivore ethics with cavemen ethics.
One views animals as pieces of meat wrapped in plastic.
The other viewed them as fellow travelers in the great gladiatorial arena of life.
[To clarify: civilization can be compatible with caveman ethics. We are mammals and observe territorial politics. Suffering/war/death are not opposed to civilization. Thinking otherwise leads to Christianity/liberalism/general faggotry]
Now if for example, Hitler had scientific proof that Jews were inferior, would this have made the Holocaust justifiable?
Certainly. The culling of an inferior path within a species is natural.
Without such proof, it still couldn't be said to be "wrong" - it's simply a natural product of mammalian politics. We live. We struggle. We die.
My problem with humans in relation to meat consumption is this: there is no struggle - and therefore no honor
. 98% of people would refuse to ever see meat again if it meant they'd have to survive being chased by a hungry tiger to reach it.
Those people do not deserve to feast on superior lifeforms.