The carnist claims that because some species eat meat, we should ethically be allowed to
Lions kill each other and each others' young. Therefore, if it happening in nature is justification, then all murder is now moral.
Other arguments involving humane slaughter, or how the breeding of animals justifies their slaughter contradict this argument since those are in direct opposition to how lions hunt. So if you argue for one you can't argue for the other.
The point is that if you're reading this, you don't need to eat meat to live. So this isn't a question of what an animal that has no choice would do. Ultimately, this argument is akin to pointing to someone else's self-defense, for instance, to justify outright murder. That sort of logic doesn't fly in any other context.
Interesting that carnists conveniently pick the lion. Let's pick an animal arguably much more similar to us, monkeys that throw their feces in an argument. Carnists don't seem keen to copy that or claim that is ethical behavior. What about humans that kill other humans? Does Ted Bundy's existence now justify all murder? After all, "Humans kill humans - it's just how it is!" and "When I look out at humans, I see them killing each other, so I can too!"
Another case of cherry-picking is how carnists consider "the hunt" as equivalent to putting meat into a shopping cart that has been extruded, ground up, and cooked. This seems like it has little resemblance to anything lion-related.