Ethics and morality are not dead otherwise we'd see anarchy everywhere and thankfully we're a long way from that.

I imagine that costco wasn't attempting to "punish" the young engaged couple for not living together. They probably have a policy which states that members of a single household can hold joint accounts. Business cards are allowed to have joint members who don't live together but individual cards only offer joint accounts for single households.

Business wise this makes sense. Otherwise everyone on the block could pay for one costco membership and have all the neighbors be "joint" members on the account. Costco would lose money.

So their intent is to limit the joint accounts to "households" to maximize their profits. To suggest they have an interest in getting young people to live together prior to marriage is frankly absurd.

The clerk most likely suggested they would have been better off if they had lied because the lie would have been somewhat inconsequential as I imagine shortly the young couple will in fact share a single residence.

Mostly I think the O.P. is making a mountain out of a molehill.