On a purely democratic basis, most humans believe meat it good for them, and will eat it when given the choice. The vegetarian movements are small, and outside religious communities, miniscule.
Intellectual property is as real as real property. A Native American would make the same argumentyou do, but levy it against the notion of real eatate: owning a plot of the earth is ridiculous.
Your argument against "nonrival" would imply that if a manufacturer creates surplus product, its ok to steal the surplus because no one else needa it.. even if they go bankrupt because no one then buys the non surplus.
And a Marxist would say that labor ia property, and its rheft to deprive a laborer of ownership of their labor. All property is a legal fiction, you cant arbitrarily decide that one kind ia legitimate and the others aren't. Rivalry is just one factor.