Actually, I've never been tempted to steal hotel towels, but this story reminds me of one time I sneaked them out of the hotel. In 2011, I attended the March Meeting of the American Physical Society, which that year was held in Dallas. I had lived near Dallas not long before this, so I welcomed the opportunity for a return visit.
Sadly, the hotel I had booked for the whole week -- a member of a mid-priced chain at which I had never had any previous problems -- was, to put it very kindly, shabby. One look at the sheets told me I wanted no physical contact with them; fortunately, there was a Walmart nearby, so I bought a sleeping bag.
The hotel's towels were no better. They were thin and not very clean-looking, so I bought a package of white wash cloths and took them to a local laundromat, where I washed them along with the larger towels I had smuggled out of the hotel. After a cycle in the washer with some bleach, they all looked clean enough to use. Of course I left them, along with the wash cloths I had bought, so I didn't subtract towels -- I added them. Likewise, I didn't have room in my luggage for a sleeping bag, so I left that, too, with a note that the cleaning staff could keep it.
And no, I don't use that chain any more.