I know what you mean, but here's my take on it.
Firstly, injecting with toxins. We need to do toxicity testing to work out safe doses to give to humans for tests. Therefore, assuming you think that it's preferable for animals to die than humans to die, this is ok.
Eating animals. I agree with you on this. It's not totally necessary. But I think humans are omnivores, although it's perfectly possible to survive on a vegetarian, and even vegan, diet. So I agree, the logic is flawed with eating animals.
But surely it can't be debated that, out of testing (drugs, not spurious cosmetics), eating, and wearing animals or animal products, the wearing of them is by far the least necessary, and also the most easily replaced by non-animal methods.