Let me overcome my instinctive repugnance for http://www.thebigquestions.com/2011/09/19/compassion-play/ long enough to address the actual substance of his argument. He says that economics permits one to replace ordinary compassion with an allegedly "higher compassion" - a sort of hyper-racinated compassion in which every element of ordinary compassion - sympathy for the suffering of a fellow person - is removed and replaced by faith in some kind of theoretical Pareto optimization.
What he likes about economics is that it enables him to remove any actual humanity from his considerations of people. This, I think, is the fundamental source of my animosity toward him and his thought. That and the fact that the logical endpoint of his thought is always indulgence of the rich and destitution for everyone else. E
His type of economics is based fundamentally on rejection of the idea of a social compact - a responsibility of people for each other. That goes against human nature, but it has an internal logic. In the wider "compassion" he thinks, we should be exactly as eager to help the people of distant countries as our own neighbors and fellow citizens.
Humans evolved to have in-group loyalty, compassion and sharing and outgroup competition and war. Can we afford to extend in-group treatment to all, or should we, as Landsburg in effect argues, treat everyone as alien.
My answer is that as long as humans breed uncontrollably, we have no choice but to divide the world into us and them. Classical liberalism's ideal of war of all against all leads to societal breakdown and destruction of its members.