The problem with “grass has almost no moral value” is not that you then need to argue the magnitude of that moral value. It’s that no matter what that magnitude is, there will be some point where enough grass becomes the most important thing morally. If you want to believe that a human always outweighs grass morally, and you believe that moral comparisons are even possible, you must believe that grass has zero morality, or your beliefs contradict themselves.
You seem to be assuming the value of grass aggregates without bound as a function of the amount of grass. Why wouldn’t there be diminishing marginal value to grass, as the amount of grass increased?
The problem with “grass has almost no moral value” is not that you then need to argue the magnitude of that moral value. It’s that no matter what that magnitude is, there will be some point where enough grass becomes the most important thing morally. If you want to believe that a human always outweighs grass morally, and you believe that moral comparisons are even possible, you must believe that grass has zero morality, or your beliefs contradict themselves.
You seem to be assuming the value of grass aggregates without bound as a function of the amount of grass. Why wouldn’t there be diminishing marginal value to grass, as the amount of grass increased?
Because that’s a variable value principle and it’s also been proposed as a solution to the Repugnant Conclusion, and it doesn’t work.