I recall first seeing a resort fee being imposed at a Marriott property (it's been so long that I cannot remember where...Miami?). This was prior to comprehensive on-line booking systems, which at least give you a preview of the fee. When I was checking out I was surprised that I was being charged for stuff I had not used and I complained to the desk clerk. He promptly removed the fee and acknowledged that it was "something new." At the same checkout desk was an Asian visitor who was, in limited English, trying to complain about the same thing. The clerk serving him told him "it's a tax. It's a government tax." He gave up. I recall being ashamed that this visitor will probably tell his friends to be wary of US hotels.
Resort fees are simply computerized bait and switch schemes. They are no more ethical than the cab driver who doubles his price for a return fare once you reach the pyramids.