Under that line of logic, we can do other things that lions do 'naturally', such as killing our offspring, stealing from others, force-ably having sex with others when they don't want it, and being violent and killing others when we are upset because we have been designed to. Natural law is not about doing what comes naturally to your design. It’s the idea that your rights as an individual are not determined by the state or through the democratic process but are derived from self-ownership or inherent within the universe.

Unlike lions, we do not require the consumption of meat in order to thrive, moreover as I'd imagine most humans tend to have more consciousness when it comes to the understanding of right and wrong, it would seem incumbent upon us to hold ourselves to a higher standard. By your analysis, if alien vampires decided to feed on human beings the way we feed on animals, it would be permissible for them to do so as it is within their nature. Your position is logically inconsistent unless you concede to this.

I'd also correct you by saying that we are behaviorally omnivores however physiologically herbivores.

There are many arguments to support this point but the most salient is that true carnivores do not suffer from atherosclerosis when consuming meat, unlike humans and other herbivores. (See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1312295/)

The fact that there are over 700+ million examples of healthy and thriving vegetarians and vegans in the world, among them world-class athletes eg Carl Lewis, Timothy Shief, Alexy voevoda, Venus Williams and the greatest minds that have ever lived e.g. Albert Einestein, Tesla, Leonardo Da Vinci, Pythagoras, Benjamin Franklin etc would make this fact self-evident.