I disagree. If I can - give $10 to the person on the corner who has a 20% chance to waste it on alcohol or drugs, or - give it to a charity that I know does g

I disagree. If I can - give $10 to the person on the corner who has a 20% chance to waste it on alcohol or drugs, or - give it to a charity that I know does good work then the second option seems better to me; and that 20% is part of the (reasonable) justification why.