I'd bet money that "we made some ridiculous claim to be able to charge you after the fact for doing something reasonable" wouldn't hold up against the chargeback.
This is the thing; in most countries, America included, 'freedom of contract' is constrained by many laws, including 'reasonableness' tests. Personally, I think this is a feature, not a bug.
[1]chargebacks are one of the things that changes how much 'reserve' the merchant account holds back... if you don't have great credit, and/or if you have chargebacks, sometimes the merchant account will hold your money for months before releasing it to you. You really want to avoid chargebacks, as a merchant.
"Item not as described" is a huge loophole to get whatever you want for free. Hopefully the card issuers track repeated abuse. The banks don't even ask for proof the item was returned. Amex is particularly brazen if you want to steal free products.