The problem is, when you have 20 people of varying abilities hacking away for their own definition of the "joy of programming" on a project, it has a tendency to collapse under its own weight.

When you've only every worked on greenfield projects, or are working on a start-up who's only aim is to sell up before they explode, then yeah, code for fun. Just make sure that you're not expected to support it for 5+ years.