Here's how I think of it. They either go to the landfill, or your house is a landfill. So you're not really saving stuff from the landfill.

I'm in the process of helping my mom sell her house and move into a small apartment. Fortunately her nearby public library takes donations. I think that they have an annual book sale and use the proceeds to support library operations.

I've gotten pretty ruthless about throwing things away. It's not too hard to follow a plan such as a cubic foot per week. The number of books that I'm emotionally attached to dwindles with time.