Let me give a concrete example from my past. We had a public API of POJO domain objects that could be used to render templated files, think string replace. It worked great until one day someone had a special character that caused it all to fail. How do you fix this? Ask all customers to clean their values? Good luck with that!! However from our side we just added the code to clean the output, escape the special character for the templating engine, and everything worked great.

The only other option was to have thousands of customers with live systems edit their templates and or data to fix that one bad character. It affected a lot of people due to another unrelated update. Anyways had we not been forcing the use of setters and getters a solution would have been on a whole other scale! And no we couldn’t edit the template engine, etc, because in most cases it was valid.