Drug Dealers, Pimps, and Prostitutes
Developers, Marketing, and Graphic Designers.
Sort of a modern day parody to the summer of love. Notice, that generation is the one in power at the moment, and things have never been so totalitarian.
And note, the Austin Powers speech does not defend it :)
The kernel and basic tools will always be free, that has been true for longer than Linux or the GPL have been around. But, where is the urge to supply free to everyone else. It is not like the average user contributes back, the contribution back happens with the tech folk.
So, to make money with opensource, you opensource to begin with, monitor the copyright ensuring it comes into your domain, get some community backing, and some people saying the software is great, then fork your own creation.
Keep the opensource tool running behind the commercial release, and accept any modifications if you get copyright, until you emerge as one of the market leaders.
Then move to a completely commercial offering, where lots of people can install your tools, and you have a good track record.
Opensource is swings and roundabouts to developers, but at some point most software will go back to being commercial, and there will always be freeware, and on the whole it has improved quite a lot.