The library is really a very good idea. I must do taht.

They also have the advantage of selling on books for a negligible price when they've finished with them.

This isn't a point in their favour right now! Though I've benefited happily from library sales in the past, I've also tended to pick up books I liked very much when I read them in the library, to be sure of instant access at all times...

Never mind, as vices go, it's a pretty cheap and convenient one

There is that. And no-one has yet to suggest that books are carcinogenic...