Not only a repulsive concept, but really bad advice.
Hotels that are fully aware that their robes are in demand will simply bill you if you take them.
I've been in several luxury hotels that left a notecard in the room saying basically this: feel free to take the robe with you, it's $149. Or simply phone us: we'll send up a brand-new one in a box for the same price.
A unique hard-bound book: I'd never take that no matter how interesting it was. I might ask the FDC where I could buy one.
Toiletries, notepads/paper, pens, and other consumable items: I don't personally consider taking that stuff "theft", and I seriously doubt the hotel does either unless it's a very unique situation (e.g., raiding the housekeeping cart for a large quantity of an item). I just assume that 80% of the ballpoint pens in regular use on Planet Earth have Marriott's brand and logo on them, and Marriott is quite pleased with this. @:-)