Richard Stallman explains why the Swedish Pirate Party platform is bad for open source, and what to do about it:
How would the Swedish Pirate Party’s platform affect copylefted free software? After five years, its source code would go into the public domain, and proprietary software developers would be able to include it in their programs. But what about the reverse case?
Proprietary software is restricted by EULAs, not just by copyright, and the users don’t have the source code. Even if copyright permits noncommercial sharing, the EULA may forbid it. In addition, the users, not having the source code, do not control what the program does when they run it. To run such a program is to surrender your freedom and give the developer control over you.
So what would be the effect of terminating this program’s copyright after 5 years? This would not require the developer to release source code, and presumably most will never do so. Users, still denied the source code, would still be unable to use the program in freedom. The program could even have a “time bomb” in it to make it stop working after 5 years, in which case the “public domain” copies would not run at all.