I think people should consider recycling books if they don't want to keep them. And by recycling, I don't mean taking them to Oxfam or a second hand bookshop, I mean putting them in the recycling bin.
What a waste! Absolutely. Not green at all. But if people don't do this, there are two problems. One is the world will gradually choke with books as more and more come into the world and fewer and fewer ever leave the circuit. The other, more serious, concern is that if someone wants to read one of my books I would far rather they either bought a new copy or borrowed it from a library. In part this is because it means I can afford to live, and in part because if people don't buy new books (which are still incredibly good value compared with cinema, theatre, opera etc.) then publishers will go bust and there will be far less good quality reading available.
There are plenty of other things you can give to and/or buy from charity shops. But please don't make it books.