And this is the flaw in your argument. Wifi bandwidth is a finite resource. If a bunch of people are stealing it then there will not be enough for those paying customers who want to use it, and then the business owner must "replace" it by paying for MORE bandwidth.

Stealing wifi codes is simply stealing. Nothing more, nothing less. Of course, if you walk in and they give you the code for the asking, that is their choice. Fine. Use it. But posting it on a forum, or sharing it around willy-nilly is no different than any other sort of theft.