Those established legal meanings (even the ones that are “objective” as that term is used in law [0]) are themselves subjective.

[0] “objective” in legal standards often refers to a subjective standard where the decision-maker is not to apply their opinion on the overt rule, but to apply their opinion of what a “reasonable person” would opine about the overt rule.

Important to note that in this case they weren't trying to define pornography but were stating that the film for the case in question was not pornographic and so Ohio couldn't infringe on the directors first amendment right to display the film.

Your framing makes it seem like they decided something was pornographic, when what they were doing was protecting free speech.

From your own source:

>I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description ["hard-core pornography"], and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that.