And have you read Singer's essay(s)? They are extremely difficult, if not impossible, to attack from a logic standpoint. This is the point of the essays. He also wrote one (Famine, Affluence, and Morality
http://www.petersingerlinks.com/famine.htm) in which the conclusion is that everyone has a moral duty to give away all of their money to the point that they are starving and freezing to death.
He makes an extremely compelling argument because he approaches the problem very logically and in a step-by-step manner. Anyhow, the point of his essays are not generally to persuade politically, but that clear and rational thought are necessary in dealing with questions of ethics, even if it leads to seemingly irrational results.