I guess I should explain what the term Fachidiot really means. According to babelfish (http://babelfish.altavista.com/) it means a specialized idiot but “Subject Matter Idiot” is probably more descriptive. Basically a fachidiot is a person who knows so much about one single thing that they know nothing about anything else.
When facing any problem a fachidiot will immediately assume that the solution can be only be found within their area of expertise. While this is human nature, and I could live with people doing stupid things because of lack of holistic understating, a fachidiot compounds the issue by being overly defensive about their solution. They often resort to intellectual bullying to force their viewpoint/solution onto other people and will ignore even prima facie evidence of their solution not working.
In software these people are easy to spot: They are the XML guru (they really like to be called guru and “mentor” other people) who solve each and every problem with XML, or the manager who calls a meeting anytime two people have to talk.
Fachidioten simply lack the ability to abstract a problem enough and do not have a broad set of tools they can apply. This is also known as the “If all you have is a hammer, everything looks like a nail.” problem.
I have the opposite problem, I know a little bit about too much stuff. My interests are diverse (military history, woodworking, fishing, hunting, sports) and I would never get bored if I stopped working tomorrow (I think people who say that are intellectual midgets). I use skills and knowledge I learn from my other interests on a daily basis to help me when I am developing a piece of software and I think that my broad range of interests make me a better developer and team member.
In general, I have found that developers who do not fit the stereotype of pasty skinned, non-athletic, socially awkward dungeon-and-dragon nerds make better developers because they apply their broad set of skills to solve problems in a single domain. They are also more fun to work with and allow me to broaden my horizon on subjects I don’t understand but am interested in.