This is good evidence that the membership checks provide value to customers by keeping the riffraff away.
It's terrible evidence that the membership requirement provides any such value. Those checks are independent of the requirement -- as you acknowledge, the guards at the door are not even empowered to turn you away if you want to go in. (That said, I'll repeat that at my Costco, there is no check at the door.)
In a better world, Costco could admit that the "membership checks" are actually there to keep the tone of the store at a certain level, not to check membership. It'd be more convenient for everyone, and also more honest.
It's terrible evidence that the membership requirement provides any such value. Those checks are independent of the requirement -- as you acknowledge, the guards at the door are not even empowered to turn you away if you want to go in. (That said, I'll repeat that at my Costco, there is no check at the door.)
In a better world, Costco could admit that the "membership checks" are actually there to keep the tone of the store at a certain level, not to check membership. It'd be more convenient for everyone, and also more honest.