One difficulty (although not the only one) that was raised when speaking of this to others at Columbia, whether other instructors, my students, or in general, is that it gives a certain authority to the rich nonetheless. In other words, only the rich have the opportunity to sell all they own and give the proceeds to the poor. This observation may be counteracted with the discussion of Lazarus and the rich man, in which Lazarus who has nothing, at death goes to Abraham's bosom, while the rich man suffers torment. Another rebuttal might be the following passage in Luke 21:1-4:
He looked up and saw the rich putting their gifts into the treasury; and he saw a poor widow put in two copper coins. And he said, "Truly I tell you, this poor widow has put in more than all of them; for they all contributed out of their abundance, but she out of her poverty put in all the living that she had."
So, the poor woman, who has only two coins, nonetheless, can follow Jesus' commands to give all one owns away, while the rich, who give out of their riches, do not put in as much as she does. You either give everything or not give everything, no matter how much that everything is. This levels the playing field a bit. Yet, there is a difference with all of the other economic issues in Luke. Everywhere else, one gives money to the poor. Here, the poor woman does not give her coppers to the poor, but to the temple treasury, and, presumably, by extension to God. Although, really, to the priests.
Interestingly enough, this passage directly precedes the prediction of the destruction of the temple: "there shall not be left here one stone upon another that will not be thrown down" (21:6). I personally do not know what to make of this juxtaposition of praising the poor woman for giving all she owns to the temple and subsequently predicting the temple's demise, shifting into rather apocalyptic language until chapter 22. So, perhaps while one economic objection is settled, a new issue arises.