In Pygmalion, what does Alfred Doolittle mean by saying "he cannot afford morals" and that "middle class morality is just an excuse" for not giving him anything?

After Eliza has been staying with Professor Higgins for a while, her father, Alfred Doolittle, calls on Higgins and Pickering. Seeing how wealthy Higgins is, he believes this is an opportunity for him to get some money from him. He offers to let Higgins keep Eliza in exchange for a "five-pound note." This prompts Pickering to exclaim, "Have you no morals, man?" Doolittle replies that he can't afford them. In other words, he's too poor to not try to take advantage of a situation that presents itself to him. In his view, someone with wealth can "afford" to have morals because he won't be tempted to do something dishonorable for a small amount of cash.
Doolittle then goes on to expound upon the burden of "middle-class morality." He admits that he is one of the "undeserving poor"—that is, someone whom society considers unworthy of financial aid because his lifestyle doesn't match with its expectations of morality. He explains how unfair the situation is. He actually has more financial needs than a moral person because he eats the same amount of food, but he drinks more and requires more entertainment. Yet he is ignored by philanthropists because they feel he's not a moral person. To him, it's unfair and nonsensical that a widow can collect donations from six different organizations in the same week "for the death of the same husband" when those donors won't give him even one gift. That's why he says that middle-class morality is just a way for charities to pass him by. It gives philanthropic groups a reason to direct their funds elsewhere.
Higgins is won over by the convoluted but intriguing logic of Doolittle. He says to Pickering, "It's a positive crime to give this chap a farthing. And yet I feel a sort of rough justice in his claim." He ends up giving him "a fiver."