If you're going to help, you have to get it straight in your mind from the start that you don't expect thanks. Or you're going to be sorely disappointed, when working with the poor, or anybody for that matter.
You are right about that. You have to give without expecting anything in return. However, you also should speak up when abuse is returned. Shaming someone who is mean to those who have shown charity is fine - not for what it does for those who have been abused; but for what it might do for the idiot who is dead to love.