I think what you're suggesting is footed on the appeal to nature fallacy. What happens in nature is natural and therefor good.

Also, I'm not sure a cephalopod has evolved the physical and mental capability to vary its diet on command such that it can choose if it will feed on other animals or not.

At some level humans and cephalopods are just animals, and equivalent in that regard, but I'm not sure I accept the equivalence far beyond that or especially when it comes to morality.