Open collaborative design/Free riders

So what about free riders? What happens when there are people who only take and never give anything back?

Well, nothing really. Contributors are not expecting quid pro quo. If it is trivial to duplicate the results of someone's efforts then the more people who make use of it and benefit, the better. The situation is not zero-sum — people are not going without as a direct result of someone else having it. Consider free and open-source software where, as an example, anyone with a computer and internet connection can download the Firefox web browser or OpenOffice office software for free. Most people will be consumers rather than contributors, but it is of no consequence.