I've just curious how the OP feels when an obese flyer sits down next to him and demands to lift the armrest. If an obese flyer were to find a trick to force the armrest to get stuck in an upright position, would the OP think that was acceptable?
People who need to lift their neighbor's armrest to fly need to buy the seat next to them. People who need to wedge the person's seat in front of them in a bolt-upright position need to buy the seat in front of them. It's as simple as that.