I accept that was not entirely a correct analogy. Try these:
take a large hollow pipe and place it on some scales, then take a bunch of helium balloons with lead weights beneath them (where the lift =weight) and float them into the tube (not touching the sides). Will the weight registered on the scales rise? Of course not. Then, with all the balloons inside, seal the tube off with flat discs at each end, any change? no. Then, by remote control (well, some how!) burst the balloons; now the weight will change.
Alternatively, take your a/c on the ground, with the wheels on scales, and get a load of tame geese to fly into the cabin through an open door. Do you think the weight on the scales will rise with each goose entering? Then close the door, no change. Then get the pilot to ask over the PA that all the geese kindly stop flying and sit down. Then the weight will rise.
Sorry about the odd situations, but it is an odd question in the first place, which seems to need simple answers. The phrases that spring to mind are "ignorance is bliss" and " a little knowledge is a dangerous thing".
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Another day in paradise