Jeza, it isn't an either/or situation for most people. Just because you have an eReader it doesn't mean you will never read a printed book again, although eReaders are a boon for those who can't manipulate paper books very well or have troublesome eyesight helped by the choice of fonts an eReader gives.
eReaders also have a big advantage as no unsold books are remaindered and pulped which is a total waste of raw materials, publishing, distribution and storage.
eBooks bought online or borrowed from a library at least sees the author getting some payment, which doesn't happen when you buy a second hand book.
No trees are harmed in the publishing of an eBook.