The authorities can just force you to install some worm (or just install that worm for you to begin with) to observe what you're using. Trojans are already installed in mobile phones in the EU/US/Israel/India uppon the order of the respective intelligence agencies, while those countries, as well as Russia and China are famous for having backdoors to any "private" company's internet gateways, so I wouldn't be surprised if they would be "required" to check what's running on your computer in order to fight "international terrorism", "tax fraud", or "child pornography" soon either.
On the topic, the open source idea wasn't born from the idea of being free of charge. In fact, the BSD licence allows commercial redistribution, and if you order a hardcopy you'll pay money for it, too. Originally you were required to posses a UNIX license to obtain BSD, and the UNIX license was worth _alot_ more then $200.
The foundation of open source software is freedom, as in freedom of choice. And the choice is about running a software or not doing so - or running a variation/alternative version, or modifying the software you were given to create a new variation on your own. I doubt having to pay (once again) would kill off OSS - it would kill a considerable market share of desktop linux though, as the majority of linux users don't care or even know about the OSS idea but only about not having to pay, and would certainly go "back" to Windows OS if their distribution was more expensive than a regular Windows copy.