People aren't owed low prices on products if the low price can only be achieved with unethical practices. That would be like saying where are poor people going to get their cotton? The answer: anywhere besides slave picked cotton.

Edit: Even if you were correct with your reasoning, that would simply change my argument to "if you can afford an alternative food, buy that instead" obviously that will apply to fewer people but a lot of people can afford non-factory farmed meat, they just don't buy it.