> The majority of people/groups I see selling Drupal stuff sell themes which I see as legitimate... It takes a lot of work to make a well-written theme
It takes an equal amount of time and effort, and in many cases significantly more, to make a module. As a developer it's hard to argue that the time spent isn't worth something. If that project is the only project worked on by a developer continued work and development may not even be possible without charging for the software. Certainly their work can then be redistributed for free, but that's a risk the developer can choose to take and offset with value added services such as official support for the module. When the module doesn't work for someone that got it for free they then also have the option of turning away support requests from that person or trying to sell them support. I don't see how this is any less legitimate than making themes.
> Isn't the point of using software like Wordpress, Drupal, Joomla, et al to be a part of a larger Open Source community?
I've been involved with a bunch of open source projects and the majority of the users don't really seem to know or care where the software came from. They care that it works the way they want. The fact that it's "free' is a bonus typically but many would willingly pay for it. That's part of the reason Red Hat makes money and other companies supporting open source make a lot of money.
> I know I would never sell a module or theme rather than release it to the community, because that's what's been done by my predecessors in the community.
That's great, and that's a choice that works for you. It likely doesn't work for everyone. One of the nice things about the GPL is that it allows each end user of the software to use it as they see fit so long as the same rights are extended to the next person it is shared with.
> There's a good thread here http://drupal.org/node/237682 discussing just this and the general consensus seems to be that it's possible but generally harmful to the community. I think this applies not only to Drupal but to every Open Source project in general.
Unfortunately that thread, like so many others, is filled with a lot of incorrect information about the GPL and it's very hard to find the valid information within all the noise. Selling open source software has worked extremely well for a large number of companies. There are and have been numerous companies that have helped grow open source communities and projects through their charging for open source software or addon services. Red Hat, Cygnus, VA (Research/Linux/Software/Whatever they are this week), etc.
I would recommend reading the gnu.org page on the philosophy of selling open source software. One of the key lines is:
> Distributing free software is an opportunity to raise funds for development. Don't waste it!
http://www.gnu.org/philosophy/selling.html