A fine idea, but there is one thing that disturbs me about this (and I fully expect to get a ration of do-do for my opinion). Taking unused soaps from the hotel for donation is essentially like me taking the change from your pocket and giving it to a charity of MY choice. If unused soaps are okay, what about the backup roll of toilet paper? or the towels? All of those items increase the expenses of the hotel increasing the cost of the room, increasing the cost to the airline, increasing the cost to our customers.
Giving toiletries to shelters is a great idea, but I submit, if one truly believes it is a good idea, rather than stealing the unused stuff from the hotel, buy them yourself (in a quick search, I found soaps at about $0.15 each... or $150 for a thousand).