They are damned if they do and and damned if they don't. If they don't then people lambast them for not utilizing their platform. If they do then they're sticking their nose into not their business and not donating enough no matter how much they donate. There's no way to win for them, then again being a public figure is a curse and guarantees there's always someone who's going to be disgruntled.
I say all publicity for a good charity is good and all giving is good. If someone makes 100K and gives 50 that's awesome, if someone makes 40k and gives 20 that's also awesome, all donations are good to a worthwhile cause and charity.