Hume's Freshly Sharpened Guillotine

Rocks cannot benefit. The surprising consequence of this is Hume's guillotine. The psychological barrier will be that if there's no ought from is, there is no ought. (Except in that if you want Y, and only X leads to Y, you ought to do X. And the surprising consequence of that is the standard moral rules.)

Rocks are not conscious, so for rocks to benefit, benefit has to be objective. This means it must be measurable. Not only must there be a benefit-measuring instrument, it would have to be necessary to take this measurement to correctly predict how a rock would behave.
Humans occasionally project minds onto mindless things, such as thinking that a rock resists breaking and is sad if it is hit hard enough to crack. However, some rocks would suffer more, others less, and the cloven halves of one rock would behave differently than another. Modus tollens, there is no benefit, and thus benefit is not objectively real.



Because benefit is subjective, value is subjective. Insert being shocked, shocked. At this point there's still a possibility of logically relating preferences to each other and finding a logic crystal, from which right and wrong could be refined. However, such a right would necessarily be objective, which would therefore have to be measurable to be real, as above.