Recycling old glasses makes people feel generous and thrifty. They believe they’re helping people and saving money. They think the glasses they donate are “free,” because they don’t consider all the hidden costs of sorting and shipping them. And they don’t realize just how cheap manufacturing new glasses has become. If they really wanted to help people see, they’d send money. Unlike leftovers, it’s guaranteed to fit.
Virginia Postrel explains why those Used Eyeglasses boxes — which seem to be everywhere — are more cruel than kind. I’d also add that these boxes also seem to exist to help induce people to spend more money — on new glasses for themselves.