Is selling WordPress services illegal?

I’ve seen and heard this before.

Since WordPress is released under the GPL license then all derivative works also have to be released under GPL. (read: free)

So what is a derivative work?

Is it a custom theme I build for a client?  Maybe…

Is it selling premium themes like WooThemes and Revolution?  Maybe…

I think it’s all such a worthless argument.  If people do work, they should be allowed to charge for it.  There’s a grey area… sure.  But expecting people to provide high quality work and on-going support merely for the “warm glow” of helping the community is ridiculous.

For a more involved discussion on the subject here.