Before I started working, all of my books came from thrift stores, library book sales, and garage sales. I didn't fathom getting my books any other way. There's quite nothing like looking through books and finding that one that's been on your wish list. And wait, it's also for 99 cents! Score! I remember finding Wicked, the creme-colored large paperback edition, for 10 cents at my university library's book sale! And how about the time I got Sylvia Plath's Unabridged Journals for free from the public library's librarian (they were culling old book copies). Finding a great book for a great price made me feel really good.
Used books give you a history when you acquire them. There's marginalia, the smell, and sometimes people have left something of themselves behind, a bookmark, a pressed flower, etc. New books give you a chance to create history.