[JamesBarney]

You could also accidentally save Hitlers life. I'm sorry if I misspoke, I didn't mean to imply it's theoretically impossible to do harm by giving people money.

You're right that it's plausible that their have existed in the world at some time charities that have accidentally done harm. I don't think that it's plausible that it's a significant problem facing charities, specifically large charities advocated by 'Effective Altruists'.