My issue with tipping housekeepers is simple. The more common it becomes for housekeepers to be tipped, the more weight the hotel industry can put behind pushes to have housekeeping classified as a tipped position. Thus requiring hotels to pay housekeepers substantially less per hour and allowing for limited raises. This would be a huge issue because there is not much a housekeeper can do in the time they are allotted per room to increase their tip. Housekeepers are unlikely to do enough rooms to get the tipping necessary to make up the difference to a living wage.
I abhor tipping. I think it is nonsense that society requires me to give a person money to make up for business owners not paying their staff a living wage. I also think it is utter madness to tip a given amount regardless of service level. It takes the mickey right out of, do a good job, get a tip mentality that started the whole thing. Plus tipping can create culture clash issues because in the majority of the World tipping is unnecessary to downright rude.