The false equivalency is that a larger car doesn't have excess car in the same way that an adult doesn't have excess human compared to a child. A larger car is not the same thing as a car that is destroyed. A car that needs fixing because you have a second car attached to the roof might be a better comparison. A mechanic would be right to recommend you remove the second car from the roof before attempting to fix it because it was never designed to carry that much car.