I disagree with American Airlines cashless inflight cabin. What do others think?

My landlord tried a no cash, (check or money order) only policy on me more than 10 years ago. I pointed out to him that each bill in US currency has "This note is legal tender for all debts, public and private" printed on the face of it and he could accept it or take me to court and be shown to be the fool he is. He backed off real quick. I think any no cash policy is asinine as well as illegal.