I believe you, doc. But one thing about this argument stumps me; namely, why would it take a small amount of energy? Maybe it could be done, but take much more energy than you could ever get out of the system? (Note I don't believe this for a second, but it seems like an obvious comeback for a person who does.)
Nobody will know until someone actually invents one. If dropping an object can generate more energy than it takes to lift it, you'll have a perpetual motion machine, but like you I don't see any reason why people should assume this to be the case. Technologically, it's far more likely that the anti-gravity machine will consume MORE energy, and that using it will be at an energy loss.
That DOESN'T mean the technology would be useless. All kinds of technologies, from spacecraft to aircraft, could make use of an all electric propulsion system based on this type of tech.
Oh, but we do have that. It's called a lever.