Once you concede that it might be Pareto efficient, you've already lost. In the real world that's never the case. No one is (a) so spiteful that they will scut

Once you concede that it might be Pareto efficient, you've already lost. In the real world that's never the case. No one is (a) so spiteful that they will scuttle their supposed productivity because they are limited to $X Billion instead of $X+Y Billion, and (b) so important that no one will produce eqivalent value in their absence.