I don't think of it as a criticism, moreso as an opportunity that people may not have fully considered. If you ask most people who do give to charity why they do it they'll usually say that they want to make a difference or alleviate suffering. As long as they aren't overly set in their ways they should be happy to hear about more effective giving opportunities, or maybe even to consider the entire question in a new framework that helps them better accomplish their stated goals.