Don't just tell them that it will make their wallet thinner like all the other bums. The idea, as any good salesman knows, is to make them believe you are doing them a favor by taking their money. People with money are frequently targeted by thieves and kidnappers. Giving will make you feel warm and fuzzy inside. Money has been associated with idleness, which can cause ill health and even death.
Money is the root of all evil.
If you get rid of your money, you won't have to pay bank fees. Having less money makes you a more prudent shopper. If you don't have any money, you don't have to figure out what to spend it on. You might lose it in the sofa if you don't give it away. You'd probably just waste it on something you don't really need.